diff --git a/.env.dist.testing b/.env.dist.testing
index c3f4d0d..e1cc30c 100644
--- a/.env.dist.testing
+++ b/.env.dist.testing
@@ -16,6 +16,7 @@ TEST_TABLE_PREFIX=wp_
 TEST_SITE_WP_URL=http://127.0.0.1
 TEST_SITE_WP_DOMAIN=127.0.0.1
 TEST_SITE_ADMIN_EMAIL=wordpress@convertkit.local
+CONVERTKIT_API_BROADCAST_ID="8697158"
 CONVERTKIT_API_FORM_ID="2765139"
 CONVERTKIT_API_LEGACY_FORM_ID="470099"
 CONVERTKIT_API_LANDING_PAGE_ID="2765196"
diff --git a/.env.example b/.env.example
index 6c14378..ed515ed 100644
--- a/.env.example
+++ b/.env.example
@@ -16,12 +16,15 @@ TEST_TABLE_PREFIX=wp_
 TEST_SITE_WP_URL=http://convertkit.local
 TEST_SITE_WP_DOMAIN=convertkit.local
 TEST_SITE_ADMIN_EMAIL=wordpress@convertkit.local
+CONVERTKIT_API_KEY=
+CONVERTKIT_API_SECRET=
 CONVERTKIT_OAUTH_ACCESS_TOKEN=
 CONVERTKIT_OAUTH_REFRESH_TOKEN=
 CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA=
 CONVERTKIT_OAUTH_REFRESH_TOKEN_NO_DATA=
 CONVERTKIT_OAUTH_CLIENT_ID=
 CONVERTKIT_OAUTH_REDIRECT_URI=
+CONVERTKIT_API_BROADCAST_ID="8697158"
 CONVERTKIT_API_FORM_ID="2765139"
 CONVERTKIT_API_LEGACY_FORM_ID="470099"
 CONVERTKIT_API_LANDING_PAGE_ID="2765196"
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 5c9844e..39442b8 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -31,6 +31,8 @@ jobs:
       DB_PASS: root
       DB_HOST: localhost
       INSTALL_PLUGINS: "woocommerce" # Don't include this repository's Plugin here.
+      CONVERTKIT_API_KEY: ${{ secrets.CONVERTKIT_API_KEY }}
+      CONVERTKIT_API_SECRET: ${{ secrets.CONVERTKIT_API_SECRET }}
       CONVERTKIT_OAUTH_ACCESS_TOKEN: ${{ secrets.CONVERTKIT_OAUTH_ACCESS_TOKEN }}
       CONVERTKIT_OAUTH_REFRESH_TOKEN: ${{ secrets.CONVERTKIT_OAUTH_REFRESH_TOKEN }}
       CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA: ${{ secrets.CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA }}
@@ -111,6 +113,8 @@ jobs:
           path: ${{ env.PLUGIN_DIR }}/.env.dist.testing
           contents: |
 
+            CONVERTKIT_API_KEY=${{ env.CONVERTKIT_API_KEY }}
+            CONVERTKIT_API_SECRET=${{ env.CONVERTKIT_API_SECRET }}
             CONVERTKIT_OAUTH_ACCESS_TOKEN=${{ env.CONVERTKIT_OAUTH_ACCESS_TOKEN }}
             CONVERTKIT_OAUTH_REFRESH_TOKEN=${{ env.CONVERTKIT_OAUTH_REFRESH_TOKEN }}
             CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA=${{ env.CONVERTKIT_OAUTH_ACCESS_TOKEN_NO_DATA }}
diff --git a/phpcs.xml b/phpcs.xml
index 1b5a14b..1e875f4 100644
--- a/phpcs.xml
+++ b/phpcs.xml
@@ -11,6 +11,9 @@
 	<!-- Exclude minified Javascript files. -->
 	<exclude-pattern>*.min.js</exclude-pattern>
 
+	<!-- Exclude traits from the PHP SDK. -->
+	<exclude-pattern>class-convertkit-api-traits.php</exclude-pattern>
+
 	<!-- Check that code meets WordPress-Extra standards. -->
 	<rule ref="WordPress-Extra">
 		<!--
diff --git a/src/class-convertkit-api-traits.php b/src/class-convertkit-api-traits.php
new file mode 100644
index 0000000..6c77045
--- /dev/null
+++ b/src/class-convertkit-api-traits.php
@@ -0,0 +1,1808 @@
+<?php
+/**
+ * ConvertKit API Traits
+ *
+ * @author ConvertKit
+ */
+
+/**
+ * ConvertKit API Traits
+ */
+trait ConvertKit_API_Traits
+{
+    /**
+     * ConvertKit OAuth Application Client ID
+     *
+     * @var string
+     */
+    protected $client_id = '';
+
+    /**
+     * ConvertKit OAuth Application Client Secret
+     *
+     * @var string
+     */
+    protected $client_secret = '';
+
+    /**
+     * Access Token
+     *
+     * @var string
+     */
+    protected $access_token = '';
+
+    /**
+     * OAuth Authorization URL
+     *
+     * @var string
+     */
+    protected $oauth_authorize_url = 'https://app.convertkit.com/oauth/authorize';
+
+    /**
+     * OAuth Token URL
+     *
+     * @var string
+     */
+    protected $oauth_token_url = 'https://api.convertkit.com/oauth/token';
+
+    /**
+     * Version of ConvertKit API
+     *
+     * @var string
+     */
+    protected $api_version = 'v4';
+
+    /**
+     * ConvertKit API URL
+     *
+     * @var string
+     */
+    protected $api_url_base = 'https://api.convertkit.com/';
+
+
+    /**
+     * Gets the current account
+     *
+     * @see https://developers.convertkit.com/v4.html#get-current-account
+     *
+     * @return false|mixed
+     */
+    public function get_account()
+    {
+        return $this->get('account');
+    }
+
+    /**
+     * Gets the account's colors
+     *
+     * @see https://developers.convertkit.com/v4.html#list-colors
+     *
+     * @return false|mixed
+     */
+    public function get_account_colors()
+    {
+        return $this->get('account/colors');
+    }
+
+    /**
+     * Gets the account's colors
+     *
+     * @param array<string, string> $colors Hex colors.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-colors
+     *
+     * @return false|mixed
+     */
+    public function update_account_colors(array $colors)
+    {
+        return $this->put(
+            'account/colors',
+            ['colors' => $colors]
+        );
+    }
+
+    /**
+     * Gets the Creator Profile
+     *
+     * @see https://developers.convertkit.com/v4.html#get-creator-profile
+     *
+     * @return false|mixed
+     */
+    public function get_creator_profile()
+    {
+        return $this->get('account/creator_profile');
+    }
+
+    /**
+     * Gets email stats
+     *
+     * @see https://developers.convertkit.com/v4.html#get-email-stats
+     *
+     * @return false|mixed
+     */
+    public function get_email_stats()
+    {
+        return $this->get('account/email_stats');
+    }
+
+    /**
+     * Gets growth stats
+     *
+     * @param \DateTime $starting Gets stats for time period beginning on this date. Defaults to 90 days ago.
+     * @param \DateTime $ending   Gets stats for time period ending on this date. Defaults to today.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-growth-stats
+     *
+     * @return false|mixed
+     */
+    public function get_growth_stats(\DateTime $starting = null, \DateTime $ending = null)
+    {
+        return $this->get(
+            'account/growth_stats',
+            [
+                'starting' => (!is_null($starting) ? $starting->format('Y-m-d') : ''),
+                'ending'   => (!is_null($ending) ? $ending->format('Y-m-d') : ''),
+            ]
+        );
+    }
+
+    /**
+     * Get forms.
+     *
+     * @param string  $status              Form status (active|archived|trashed|all).
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_forms(
+        string $status = 'active',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'forms',
+            $this->build_total_count_and_pagination_params(
+                [
+                    'type'   => 'embed',
+                    'status' => $status,
+                ],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Get landing pages.
+     *
+     * @param string  $status              Form status (active|archived|trashed|all).
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_landing_pages(
+        string $status = 'active',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'forms',
+            $this->build_total_count_and_pagination_params(
+                [
+                    'type'   => 'hosted',
+                    'status' => $status,
+                ],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Adds a subscriber to a form by email address
+     *
+     * @param integer $form_id       Form ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_form_by_email(int $form_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('forms/%s/subscribers', $form_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Adds a subscriber to a form by subscriber ID
+     *
+     * @param integer $form_id       Form ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form
+     *
+     * @since 2.0.0
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_form(int $form_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('forms/%s/subscribers/%s', $form_id, $subscriber_id));
+    }
+
+    /**
+     * List subscribers for a form
+     *
+     * @param integer   $form_id             Form ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
+     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-form
+     *
+     * @return false|mixed
+     */
+    public function get_form_subscriptions(
+        int $form_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $added_after = null,
+        \DateTime $added_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($added_after)) {
+            $options['added_after'] = $added_after->format('Y-m-d');
+        }
+        if (!is_null($added_before)) {
+            $options['added_before'] = $added_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('forms/%s/subscribers', $form_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Gets sequences
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-sequences
+     *
+     * @return false|mixed
+     */
+    public function get_sequences(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'sequences',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Adds a subscriber to a sequence by email address
+     *
+     * @param integer $sequence_id   Sequence ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_sequence_by_email(int $sequence_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('sequences/%s/subscribers', $sequence_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Adds a subscriber to a sequence by subscriber ID
+     *
+     * @param integer $sequence_id   Sequence ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence
+     *
+     * @since 2.0.0
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_sequence(int $sequence_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('sequences/%s/subscribers/%s', $sequence_id, $subscriber_id));
+    }
+
+    /**
+     * List subscribers for a sequence
+     *
+     * @param integer   $sequence_id         Sequence ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
+     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-sequence
+     *
+     * @return false|mixed
+     */
+    public function get_sequence_subscriptions(
+        int $sequence_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $added_after = null,
+        \DateTime $added_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($added_after)) {
+            $options['added_after'] = $added_after->format('Y-m-d');
+        }
+        if (!is_null($added_before)) {
+            $options['added_before'] = $added_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('sequences/%s/subscribers', $sequence_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List tags.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-tags
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_tags(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'tags',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a tag.
+     *
+     * @param string $tag Tag Name.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-tag
+     *
+     * @return false|mixed
+     */
+    public function create_tag(string $tag)
+    {
+        return $this->post(
+            'tags',
+            ['name' => $tag]
+        );
+    }
+
+    /**
+     * Creates multiple tags.
+     *
+     * @param array<int,string> $tags         Tag Names.
+     * @param string            $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 1.1.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-tags
+     *
+     * @return false|mixed
+     */
+    public function create_tags(array $tags, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = [
+            'tags' => [],
+        ];
+        foreach ($tags as $i => $tag) {
+            $options['tags'][] = [
+                'name' => (string) $tag,
+            ];
+        }
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/tags',
+            $options
+        );
+    }
+
+    /**
+     * Tags a subscriber with the given existing Tag.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function tag_subscriber_by_email(int $tag_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('tags/%s/subscribers', $tag_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Tags a subscriber by subscriber ID with the given existing Tag.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber
+     *
+     * @return false|mixed
+     */
+    public function tag_subscriber(int $tag_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
+    }
+
+    /**
+     * Removes a tag from a subscriber.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber
+     *
+     * @return false|mixed
+     */
+    public function remove_tag_from_subscriber(int $tag_id, int $subscriber_id)
+    {
+        return $this->delete(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
+    }
+
+    /**
+     * Removes a tag from a subscriber by email address.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param string  $email_address Subscriber email address.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function remove_tag_from_subscriber_by_email(int $tag_id, string $email_address)
+    {
+        return $this->delete(
+            sprintf('tags/%s/subscribers', $tag_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * List subscribers for a tag
+     *
+     * @param integer   $tag_id              Tag ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $tagged_after        Filter subscribers who have been tagged after this date.
+     * @param \DateTime $tagged_before       Filter subscribers who have been tagged before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-tag
+     *
+     * @return false|mixed
+     */
+    public function get_tag_subscriptions(
+        int $tag_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $tagged_after = null,
+        \DateTime $tagged_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($tagged_after)) {
+            $options['tagged_after'] = $tagged_after->format('Y-m-d');
+        }
+        if (!is_null($tagged_before)) {
+            $options['tagged_before'] = $tagged_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('tags/%s/subscribers', $tag_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List email templates.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-email-templates
+     *
+     * @return false|mixed
+     */
+    public function get_email_templates(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'email_templates',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List subscribers.
+     *
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param string    $email_address       Search susbcribers by email address. This is an exact match search.
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $updated_after       Filter subscribers who have been updated after this date.
+     * @param \DateTime $updated_before      Filter subscribers who have been updated before this date.
+     * @param string    $sort_field          Sort Field (id|updated_at|cancelled_at).
+     * @param string    $sort_order          Sort Order (asc|desc).
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers
+     *
+     * @return false|mixed
+     */
+    public function get_subscribers(
+        string $subscriber_state = 'active',
+        string $email_address = '',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $updated_after = null,
+        \DateTime $updated_before = null,
+        string $sort_field = 'id',
+        string $sort_order = 'desc',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!empty($email_address)) {
+            $options['email_address'] = $email_address;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($updated_after)) {
+            $options['updated_after'] = $updated_after->format('Y-m-d');
+        }
+        if (!is_null($updated_before)) {
+            $options['updated_before'] = $updated_before->format('Y-m-d');
+        }
+        if (!empty($sort_field)) {
+            $options['sort_field'] = $sort_field;
+        }
+        if (!empty($sort_order)) {
+            $options['sort_order'] = $sort_order;
+        }
+
+        // Send request.
+        return $this->get(
+            'subscribers',
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Create a subscriber.
+     *
+     * Behaves as an upsert. If a subscriber with the provided email address does not exist,
+     * it creates one with the specified first name and state. If a subscriber with the provided
+     * email address already exists, it updates the first name.
+     *
+     * @param string                $email_address    Email Address.
+     * @param string                $first_name       First Name.
+     * @param string                $subscriber_state Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param array<string, string> $fields           Custom Fields.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-subscriber
+     *
+     * @return mixed
+     */
+    public function create_subscriber(
+        string $email_address,
+        string $first_name = '',
+        string $subscriber_state = '',
+        array $fields = []
+    ) {
+        // Build parameters.
+        $options = ['email_address' => $email_address];
+
+        if (!empty($first_name)) {
+            $options['first_name'] = $first_name;
+        }
+        if (!empty($subscriber_state)) {
+            $options['state'] = $subscriber_state;
+        }
+        if (count($fields)) {
+            $options['fields'] = $fields;
+        }
+
+        // Send request.
+        return $this->post(
+            'subscribers',
+            $options
+        );
+    }
+
+    /**
+     * Create multiple subscribers.
+     *
+     * @param array<int,array<string,string>> $subscribers  Subscribers.
+     * @param string                          $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-subscribers
+     *
+     * @return mixed
+     */
+    public function create_subscribers(array $subscribers, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = ['subscribers' => $subscribers];
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/subscribers',
+            $options
+        );
+    }
+
+    /**
+     * Get the ConvertKit subscriber ID associated with email address if it exists.
+     * Return false if subscriber not found.
+     *
+     * @param string $email_address Email Address.
+     *
+     * @throws \InvalidArgumentException If the email address is not a valid email format.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
+     *
+     * @return false|integer
+     */
+    public function get_subscriber_id(string $email_address)
+    {
+        $subscribers = $this->get(
+            'subscribers',
+            ['email_address' => $email_address]
+        );
+
+        if (!count($subscribers->subscribers)) {
+            return false;
+        }
+
+        // Return the subscriber's ID.
+        return $subscribers->subscribers[0]->id;
+    }
+
+    /**
+     * Get subscriber by id
+     *
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
+     *
+     * @return false|integer
+     */
+    public function get_subscriber(int $subscriber_id)
+    {
+        return $this->get(sprintf('subscribers/%s', $subscriber_id));
+    }
+
+    /**
+     * Updates the information for a single subscriber.
+     *
+     * @param integer               $subscriber_id Existing Subscriber ID.
+     * @param string                $first_name    New First Name.
+     * @param string                $email_address New Email Address.
+     * @param array<string, string> $fields        Updated Custom Fields.
+     *
+     * @see https://developers.convertkit.com/v4.html#update-a-subscriber
+     *
+     * @return false|mixed
+     */
+    public function update_subscriber(
+        int $subscriber_id,
+        string $first_name = '',
+        string $email_address = '',
+        array $fields = []
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($first_name)) {
+            $options['first_name'] = $first_name;
+        }
+        if (!empty($email_address)) {
+            $options['email_address'] = $email_address;
+        }
+        if (!empty($fields)) {
+            $options['fields'] = $fields;
+        }
+
+        // Send request.
+        return $this->put(
+            sprintf('subscribers/%s', $subscriber_id),
+            $options
+        );
+    }
+
+    /**
+     * Unsubscribe an email address.
+     *
+     * @param string $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
+     *
+     * @return false|object
+     */
+    public function unsubscribe_by_email(string $email_address)
+    {
+        return $this->post(
+            sprintf(
+                'subscribers/%s/unsubscribe',
+                $this->get_subscriber_id($email_address)
+            )
+        );
+    }
+
+    /**
+     * Unsubscribe the given subscriber ID.
+     *
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
+     *
+     * @return false|object
+     */
+    public function unsubscribe(int $subscriber_id)
+    {
+        return $this->post(sprintf('subscribers/%s/unsubscribe', $subscriber_id));
+    }
+
+    /**
+     * Get a list of the tags for a subscriber.
+     *
+     * @param integer $subscriber_id       Subscriber ID.
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-tags-for-a-subscriber
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_subscriber_tags(
+        int $subscriber_id,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            sprintf('subscribers/%s/tags', $subscriber_id),
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List broadcasts.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-broadcasts
+     *
+     * @return false|mixed
+     */
+    public function get_broadcasts(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'broadcasts',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a broadcast.
+     *
+     * @param string               $subject           The broadcast email's subject.
+     * @param string               $content           The broadcast's email HTML content.
+     * @param string               $description       An internal description of this broadcast.
+     * @param boolean              $public            Specifies whether or not this is a public post.
+     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
+     *                                                only to public posts).
+     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
+     *                                                a draft broadcast. If set to a future time, this is the time that
+     *                                                the broadcast will be scheduled to send.
+     * @param string               $email_address     Sending email address; leave blank to use your account's
+     *                                                default sending email address.
+     * @param string               $email_template_id ID of the email template to use; leave blank to use your
+     *                                                account's default email template.
+     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
+     *                                                (applicable only to public posts).
+     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
+     *                                                post (applicable only to public posts).
+     * @param string               $preview_text      Specify the preview text of the email.
+     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-broadcast
+     *
+     * @return false|object
+     */
+    public function create_broadcast(
+        string $subject = '',
+        string $content = '',
+        string $description = '',
+        bool $public = false,
+        \DateTime $published_at = null,
+        \DateTime $send_at = null,
+        string $email_address = '',
+        string $email_template_id = '',
+        string $thumbnail_alt = '',
+        string $thumbnail_url = '',
+        string $preview_text = '',
+        array $subscriber_filter = []
+    ) {
+        $options = [
+            'email_template_id' => $email_template_id,
+            'email_address'     => $email_address,
+            'content'           => $content,
+            'description'       => $description,
+            'public'            => $public,
+            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
+            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
+            'thumbnail_alt'     => $thumbnail_alt,
+            'thumbnail_url'     => $thumbnail_url,
+            'preview_text'      => $preview_text,
+            'subject'           => $subject,
+        ];
+        if (count($subscriber_filter)) {
+            $options['subscriber_filter'] = $subscriber_filter;
+        }
+
+        // Iterate through options, removing blank entries.
+        foreach ($options as $key => $value) {
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        // If the post isn't public, remove some options that don't apply.
+        if (!$public) {
+            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
+        }
+
+        // Send request.
+        return $this->post(
+            'broadcasts',
+            $options
+        );
+    }
+
+    /**
+     * Retrieve a specific broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-broadcast
+     *
+     * @return false|object
+     */
+    public function get_broadcast(int $id)
+    {
+        return $this->get(sprintf('broadcasts/%s', $id));
+    }
+
+    /**
+     * Get the statistics (recipient count, open rate, click rate, unsubscribe count,
+     * total clicks, status, and send progress) for a specific broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-stats
+     *
+     * @return false|object
+     */
+    public function get_broadcast_stats(int $id)
+    {
+        return $this->get(sprintf('broadcasts/%s/stats', $id));
+    }
+
+    /**
+     * Updates a broadcast.
+     *
+     * @param integer              $id                Broadcast ID.
+     * @param string               $subject           The broadcast email's subject.
+     * @param string               $content           The broadcast's email HTML content.
+     * @param string               $description       An internal description of this broadcast.
+     * @param boolean              $public            Specifies whether or not this is a public post.
+     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
+     *                                                only to public posts).
+     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
+     *                                                a draft broadcast. If set to a future time, this is the time that
+     *                                                the broadcast will be scheduled to send.
+     * @param string               $email_address     Sending email address; leave blank to use your account's
+     *                                                default sending email address.
+     * @param string               $email_template_id ID of the email template to use; leave blank to use your
+     *                                                account's default email template.
+     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
+     *                                                (applicable only to public posts).
+     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
+     *                                                post (applicable only to public posts).
+     * @param string               $preview_text      Specify the preview text of the email.
+     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
+     *
+     * @see https://developers.convertkit.com/#create-a-broadcast
+     *
+     * @return false|object
+     */
+    public function update_broadcast(
+        int $id,
+        string $subject = '',
+        string $content = '',
+        string $description = '',
+        bool $public = false,
+        \DateTime $published_at = null,
+        \DateTime $send_at = null,
+        string $email_address = '',
+        string $email_template_id = '',
+        string $thumbnail_alt = '',
+        string $thumbnail_url = '',
+        string $preview_text = '',
+        array $subscriber_filter = []
+    ) {
+        $options = [
+            'email_template_id' => $email_template_id,
+            'email_address'     => $email_address,
+            'content'           => $content,
+            'description'       => $description,
+            'public'            => $public,
+            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
+            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
+            'thumbnail_alt'     => $thumbnail_alt,
+            'thumbnail_url'     => $thumbnail_url,
+            'preview_text'      => $preview_text,
+            'subject'           => $subject,
+        ];
+        if (count($subscriber_filter)) {
+            $options['subscriber_filter'] = $subscriber_filter;
+        }
+
+        // Iterate through options, removing blank entries.
+        foreach ($options as $key => $value) {
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        // If the post isn't public, remove some options that don't apply.
+        if (!$public) {
+            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
+        }
+
+        // Send request.
+        return $this->put(
+            sprintf('broadcasts/%s', $id),
+            $options
+        );
+    }
+
+    /**
+     * Deletes an existing broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#delete-a-broadcast
+     *
+     * @return false|object
+     */
+    public function delete_broadcast(int $id)
+    {
+        return $this->delete(sprintf('broadcasts/%s', $id));
+    }
+
+    /**
+     * List webhooks.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-webhooks
+     *
+     * @return false|mixed
+     */
+    public function get_webhooks(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'webhooks',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a webhook that will be called based on the chosen event types.
+     *
+     * @param string $url       URL to receive event.
+     * @param string $event     Event to subscribe to.
+     * @param string $parameter Optional parameter depending on the event.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-webhook
+     *
+     * @throws \InvalidArgumentException If the event is not supported.
+     *
+     * @return false|object
+     */
+    public function create_webhook(string $url, string $event, string $parameter = '')
+    {
+        // Depending on the event, build the required event array structure.
+        switch ($event) {
+            case 'subscriber.subscriber_activate':
+            case 'subscriber.subscriber_unsubscribe':
+            case 'subscriber.subscriber_bounce':
+            case 'subscriber.subscriber_complain':
+            case 'purchase.purchase_create':
+                $eventData = ['name' => $event];
+                break;
+
+            case 'subscriber.form_subscribe':
+                $eventData = [
+                    'name'    => $event,
+                    'form_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.course_subscribe':
+            case 'subscriber.course_complete':
+                $eventData = [
+                    'name'      => $event,
+                    'course_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.link_click':
+                $eventData = [
+                    'name'            => $event,
+                    'initiator_value' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.product_purchase':
+                $eventData = [
+                    'name'       => $event,
+                    'product_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.tag_add':
+            case 'subscriber.tag_remove':
+                $eventData = [
+                    'name'   => $event,
+                    'tag_id' => $parameter,
+                ];
+                break;
+
+            default:
+                throw new \InvalidArgumentException(sprintf('The event %s is not supported', $event));
+        }//end switch
+
+        // Send request.
+        return $this->post(
+            'webhooks',
+            [
+                'target_url' => $url,
+                'event'      => $eventData,
+            ]
+        );
+    }
+
+    /**
+     * Deletes an existing webhook.
+     *
+     * @param integer $id Webhook ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#delete-a-webhook
+     *
+     * @return false|object
+     */
+    public function delete_webhook(int $id)
+    {
+        return $this->delete(sprintf('webhooks/%s', $id));
+    }
+
+    /**
+     * List custom fields.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-custom-fields
+     *
+     * @return false|mixed
+     */
+    public function get_custom_fields(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'custom_fields',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a custom field.
+     *
+     * @param string $label Custom Field label.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-custom-field
+     *
+     * @return false|object
+     */
+    public function create_custom_field(string $label)
+    {
+        return $this->post(
+            'custom_fields',
+            ['label' => $label]
+        );
+    }
+
+    /**
+     * Creates multiple custom fields.
+     *
+     * @param array<string> $labels       Custom Fields labels.
+     * @param string        $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-custom-fields
+     *
+     * @return false|object
+     */
+    public function create_custom_fields(array $labels, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = [
+            'custom_fields' => [],
+        ];
+        foreach ($labels as $i => $label) {
+            $options['custom_fields'][] = [
+                'label' => (string) $label,
+            ];
+        }
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/custom_fields',
+            $options
+        );
+    }
+
+    /**
+     * Updates an existing custom field.
+     *
+     * @param integer $id    Custom Field ID.
+     * @param string  $label Updated Custom Field label.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#update-a-custom-field
+     *
+     * @return false|object
+     */
+    public function update_custom_field(int $id, string $label)
+    {
+        return $this->put(
+            sprintf('custom_fields/%s', $id),
+            ['label' => $label]
+        );
+    }
+
+    /**
+     * Deletes an existing custom field.
+     *
+     * @param integer $id Custom Field ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/#destroy-field
+     *
+     * @return false|object
+     */
+    public function delete_custom_field(int $id)
+    {
+        return $this->delete(sprintf('custom_fields/%s', $id));
+    }
+
+    /**
+     * List purchases.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-purchases
+     *
+     * @return false|mixed
+     */
+    public function get_purchases(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'purchases',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Retuns a specific purchase.
+     *
+     * @param integer $purchase_id Purchase ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-purchase
+     *
+     * @return false|object
+     */
+    public function get_purchase(int $purchase_id)
+    {
+        return $this->get(sprintf('purchases/%s', $purchase_id));
+    }
+
+    /**
+     * Creates a purchase.
+     *
+     * @param string                         $email_address    Email Address.
+     * @param string                         $transaction_id   Transaction ID.
+     * @param array<string,int|float|string> $products         Products.
+     * @param string                         $currency         ISO Currency Code.
+     * @param string                         $first_name       First Name.
+     * @param string                         $status           Order Status.
+     * @param float                          $subtotal         Subtotal.
+     * @param float                          $tax              Tax.
+     * @param float                          $shipping         Shipping.
+     * @param float                          $discount         Discount.
+     * @param float                          $total            Total.
+     * @param \DateTime                      $transaction_time Transaction date and time.
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-purchase
+     *
+     * @return false|object
+     */
+    public function create_purchase(
+        string $email_address,
+        string $transaction_id,
+        array $products,
+        string $currency = 'USD',
+        string $first_name = null,
+        string $status = null,
+        float $subtotal = 0,
+        float $tax = 0,
+        float $shipping = 0,
+        float $discount = 0,
+        float $total = 0,
+        \DateTime $transaction_time = null
+    ) {
+        // Build parameters.
+        $options = [
+            // Required fields.
+            'email_address'    => $email_address,
+            'transaction_id'   => $transaction_id,
+            'products'         => $products,
+            'currency'         => $currency, // Required, but if not provided, API will default to USD.
+
+            // Optional fields.
+            'first_name'       => $first_name,
+            'status'           => $status,
+            'subtotal'         => $subtotal,
+            'tax'              => $tax,
+            'shipping'         => $shipping,
+            'discount'         => $discount,
+            'total'            => $total,
+            'transaction_time' => (!is_null($transaction_time) ? $transaction_time->format('Y-m-d H:i:s') : ''),
+        ];
+
+        // Iterate through options, removing blank and null entries.
+        foreach ($options as $key => $value) {
+            if (is_null($value)) {
+                unset($options[$key]);
+                continue;
+            }
+
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        return $this->post('purchases', $options);
+    }
+
+    /**
+     * List segments.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-segments
+     *
+     * @return false|mixed
+     */
+    public function get_segments(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'segments',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Converts any relative URls to absolute, fully qualified HTTP(s) URLs for the given
+     * DOM Elements.
+     *
+     * @param \DOMNodeList<\DOMElement> $elements  Elements.
+     * @param string                    $attribute HTML Attribute.
+     * @param string                    $url       Absolute URL to prepend to relative URLs.
+     *
+     * @since 1.0.0
+     *
+     * @return void
+     */
+    public function convert_relative_to_absolute_urls(\DOMNodeList $elements, string $attribute, string $url) // phpcs:ignore Squiz.Commenting.FunctionComment.IncorrectTypeHint, Generic.Files.LineLength.TooLong
+    {
+        // Anchor hrefs.
+        foreach ($elements as $element) {
+            // Skip if the attribute's value is empty.
+            if (empty($element->getAttribute($attribute))) {
+                continue;
+            }
+
+            // Skip if the attribute's value is a fully qualified URL.
+            if (filter_var($element->getAttribute($attribute), FILTER_VALIDATE_URL)) {
+                continue;
+            }
+
+            // Skip if this is a Google Font CSS URL.
+            if (strpos($element->getAttribute($attribute), '//fonts.googleapis.com') !== false) {
+                continue;
+            }
+
+            // If here, the attribute's value is a relative URL, missing the http(s) and domain.
+            // Prepend the URL to the attribute's value.
+            $element->setAttribute($attribute, $url . $element->getAttribute($attribute));
+        }
+    }
+
+    /**
+     * Strips <html>, <head> and <body> opening and closing tags from the given markup,
+     * as well as the Content-Type meta tag we might have added in get_html().
+     *
+     * @param string $markup HTML Markup.
+     *
+     * @since 1.0.0
+     *
+     * @return string              HTML Markup
+     */
+    public function strip_html_head_body_tags(string $markup)
+    {
+        $markup = str_replace('<html>', '', $markup);
+        $markup = str_replace('</html>', '', $markup);
+        $markup = str_replace('<head>', '', $markup);
+        $markup = str_replace('</head>', '', $markup);
+        $markup = str_replace('<body>', '', $markup);
+        $markup = str_replace('</body>', '', $markup);
+        $markup = str_replace('<meta http-equiv="Content-Type" content="text/html; charset=utf-8">', '', $markup);
+
+        return $markup;
+    }
+
+    /**
+     * Adds total count and pagination parameters to the given array of existing API parameters.
+     *
+     * @param array<string, string|integer|bool> $params              API parameters.
+     * @param boolean                            $include_total_count Return total count of records.
+     * @param string                             $after_cursor        Return results after the given pagination cursor.
+     * @param string                             $before_cursor       Return results before the given pagination cursor.
+     * @param integer                            $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @return array<string, string|integer|bool>
+     */
+    private function build_total_count_and_pagination_params(
+        array $params = [],
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        $params['include_total_count'] = $include_total_count;
+        if (!empty($after_cursor)) {
+            $params['after'] = $after_cursor;
+        }
+        if (!empty($before_cursor)) {
+            $params['before'] = $before_cursor;
+        }
+        if (!empty($per_page)) {
+            $params['per_page'] = $per_page;
+        }
+
+        return $params;
+    }
+
+    /**
+     * Performs a GET request to the API.
+     *
+     * @param string                                                             $endpoint API Endpoint.
+     * @param array<string, int|string|boolean|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function get(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'GET', $args);
+    }
+
+    /**
+     * Performs a POST request to the API.
+     *
+     * @param string                                                                                                     $endpoint API Endpoint.
+     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function post(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'POST', $args);
+    }
+
+    /**
+     * Performs a PUT request to the API.
+     *
+     * @param string                                                              $endpoint API Endpoint.
+     * @param array<string, bool|integer|string|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function put(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'PUT', $args);
+    }
+
+    /**
+     * Performs a DELETE request to the API.
+     *
+     * @param string                                                     $endpoint API Endpoint.
+     * @param array<string, int|string|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function delete(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'DELETE', $args);
+    }
+
+    /**
+     * Performs an API request.
+     *
+     * @param string                                                                                                     $endpoint API Endpoint.
+     * @param string                                                                                                     $method   Request method.
+     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
+     *
+     * @throws \Exception If JSON encoding arguments failed.
+     *
+     * @return false|mixed
+     */
+    abstract public function request(string $endpoint, string $method, array $args = []);
+
+    /**
+     * Returns the headers to use in an API request.
+     *
+     * @param string  $type Accept and Content-Type Headers.
+     * @param boolean $auth Include authorization header.
+     *
+     * @since 2.0.0
+     *
+     * @return array<string,string>
+     */
+    abstract public function get_request_headers(string $type = 'application/json', bool $auth = true);
+
+    /**
+     * Returns the maximum amount of time to wait for
+     * a response to the request before exiting.
+     *
+     * @since 2.0.0
+     *
+     * @return integer     Timeout, in seconds.
+     */
+    abstract public function get_timeout();
+
+    /**
+     * Returns the user agent string to use in all HTTP requests.
+     *
+     * @since 2.0.0
+     *
+     * @return string
+     */
+    abstract public function get_user_agent();
+}
diff --git a/src/class-convertkit-api.php b/src/class-convertkit-api.php
index 5aba61b..059ddcf 100644
--- a/src/class-convertkit-api.php
+++ b/src/class-convertkit-api.php
@@ -14,55 +14,35 @@
  */
 class ConvertKit_API {
 
-	/**
-	 * ConvertKit API Key
-	 *
-	 * @var bool|string
-	 */
-	protected $api_key = false;
+	use ConvertKit_API_Traits;
 
 	/**
-	 * ConvertKit API Secret
+	 * The SDK version.
 	 *
-	 * @var bool|string
+	 * @var string
 	 */
-	protected $api_secret = false;
+	public const VERSION = '2.0.0';
 
 	/**
-	 * ConvertKit OAuth Application Client ID
-	 *
-	 * @since   2.0.0
+	 * ConvertKit API Key
 	 *
-	 * @var bool|string.
+	 * @var bool|string
 	 */
-	protected $client_id = false;
+	protected $api_key = false;
 
 	/**
-	 * ConvertKit OAuth Redirect URI
-	 *
-	 * @since   2.0.0
+	 * Redirect URI.
 	 *
-	 * @var bool|string.
+	 * @var     bool|string
 	 */
 	protected $redirect_uri = false;
 
 	/**
-	 * Access Token
+	 * Refresh token.
 	 *
-	 * @since   2.0.0
-	 *
-	 * @var bool|string
-	 */
-	protected $access_token = '';
-
-	/**
-	 * Refresh Token
-	 *
-	 * @since   2.0.0
-	 *
-	 * @var bool|string
+	 * @var     bool|string
 	 */
-	protected $refresh_token = '';
+	protected $refresh_token = false;
 
 	/**
 	 * Optional context of the request.
@@ -106,29 +86,6 @@ class ConvertKit_API {
 	 */
 	protected $plugin_version;
 
-	/**
-	 * OAuth Authorization URL
-	 *
-	 * @since   2.0.0
-	 *
-	 * @var string
-	 */
-	protected $oauth_authorize_url = 'https://app.convertkit.com/oauth/authorize';
-
-	/**
-	 * Version of ConvertKit API
-	 *
-	 * @var string
-	 */
-	protected $api_version = 'v4';
-
-	/**
-	 * ConvertKit API URL
-	 *
-	 * @var string
-	 */
-	protected $api_url_base = 'https://api.convertkit.com/';
-
 	/**
 	 * ConvertKit API endpoints that use the /oauth/ namespace
 	 * i.e. https://api.convertkit.com/oauth/endpoint
@@ -152,10 +109,11 @@ class ConvertKit_API {
 	protected $api_endpoints_wordpress = array(
 		'posts',
 		'products',
-		'profile',
+		'profile/',
 		'recommendations_script',
 		'subscriber_authentication/send_code',
 		'subscriber_authentication/verify',
+		'accounts/oauth_access_token',
 	);
 
 	/**
@@ -445,873 +403,62 @@ public function get_access_token( $authorization_code ) {
 	 * Fetches a new access token using the supplied refresh token.
 	 *
 	 * @since   2.0.0
-	 */
-	public function refresh_token() {
-
-		$result = $this->post(
-			'token',
-			array(
-				'client_id'     => $this->client_id,
-				'grant_type'    => 'refresh_token',
-				'refresh_token' => $this->refresh_token,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $result ) ) {
-			$this->log( 'API: Error: ' . $result->get_error_message() );
-			return $result;
-		}
-
-		// Update the access and refresh tokens in this class.
-		$this->access_token  = $result['access_token'];
-		$this->refresh_token = $result['refresh_token'];
-
-		/**
-		 * Perform any actions with the new access token, such as saving it.
-		 *
-		 * @since   2.0.0
-		 *
-		 * @param   array   $result     Access Token, Refresh Token, Expiry, Bearer and Scope.
-		 * @param   string  $client_id  OAUth Client ID.
-		 */
-		do_action( 'convertkit_api_refresh_token', $result, $this->client_id );
-
-		// Return.
-		return $result;
-
-	}
-
-	/**
-	 * Gets account information from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function account() {
-
-		$this->log( 'API: account()' );
-
-		return $this->get( 'account' );
-
-	}
-
-	/**
-	 * Gets all subscription forms from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function get_subscription_forms() {
-
-		$this->log( 'API: get_subscription_forms()' );
-
-		// Send request.
-		return $this->get(
-			'subscription_forms',
-			array(
-				'api_key' => $this->api_key,
-			)
-		);
-
-	}
-
-	/**
-	 * Gets all forms from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function get_forms() {
-
-		$this->log( 'API: get_forms()' );
-
-		// Get all forms and landing pages from the API.
-		$forms = $this->get_forms_landing_pages();
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $forms ) ) {
-			$this->log( 'API: get_forms(): Error: ' . $forms->get_error_message() );
-			return $forms;
-		}
-
-		return $forms['forms'];
-
-	}
-
-	/**
-	 * Subscribes an email address to a form.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int    $form_id       Form ID.
-	 * @param   string $email      Email Address.
-	 * @param   string $first_name First Name.
-	 * @param   mixed  $fields     Custom Fields (false|array).
-	 * @param   mixed  $tag_ids    Tags (false|array).
-	 * @return  WP_Error|array
-	 */
-	public function form_subscribe( $form_id, $email, $first_name = '', $fields = false, $tag_ids = false ) {
-
-		// Backward compat. if $email is an array comprising of email and name keys.
-		if ( is_array( $email ) ) { // @phpstan-ignore-line.
-			_deprecated_function( __FUNCTION__, '1.2.1', 'form_subscribe( $form_id, $email, $first_name )' );
-			$first_name = $email['name'];
-			$email      = $email['email'];
-		}
-
-		$this->log( 'API: form_subscribe(): [ form_id: ' . $form_id . ', email: ' . $email . ', first_name: ' . $this->mask_string( $first_name ) . ' ]' );
-
-		// Sanitize some parameters.
-		$form_id    = absint( $form_id );
-		$email      = trim( $email );
-		$first_name = trim( $first_name );
-
-		// Return error if no Form ID or email address is specified.
-		if ( empty( $form_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'form_subscribe_form_id_empty' ) );
-		}
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'form_subscribe_email_empty' ) );
-		}
-
-		// Build request parameters.
-		$params = array(
-			'api_key'    => $this->api_key,
-			'email'      => $email,
-			'first_name' => $first_name,
-		);
-		if ( $fields ) {
-			$params['fields'] = $fields;
-		}
-		if ( $tag_ids ) {
-			$params['tags'] = $tag_ids;
-		}
-
-		// Send request.
-		$response = $this->post( 'forms/' . $form_id . '/subscribe', $params );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: form_subscribe(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully subscribed to the form.
-		 *
-		 * @since   1.2.1
-		 *
-		 * @param   array   $response   API Response
-		 * @param   int     $form_id    Form ID
-		 * @param   string  $email      Email Address
-		 * @param   string  $first_name First Name
-		 * @param   mixed   $fields     Custom Fields (false|array)
-		 * @param   mixed   $tag_ids    Tags (false|array)
-		 */
-		do_action( 'convertkit_api_form_subscribe_success', $response, $form_id, $email, $first_name, $fields, $tag_ids );
-
-		return $response;
-
-	}
-
-	/**
-	 * Gets all landing pages from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function get_landing_pages() {
-
-		$this->log( 'API: get_landing_pages()' );
-
-		// Get all forms and landing pages from the API.
-		$forms = $this->get_forms_landing_pages();
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $forms ) ) {
-			$this->log( 'API: get_landing_pages(): Error: ' . $forms->get_error_message() );
-			return $forms;
-		}
-
-		return $forms['landing_pages'];
-
-	}
-
-	/**
-	 * Fetches all sequences from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function get_sequences() {
-
-		$this->log( 'API: get_sequences()' );
-
-		$sequences = array();
-
-		// Send request.
-		$response = $this->get(
-			'sequences',
-			array(
-				'api_key' => $this->api_key,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_sequences(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		// If the response isn't an array as we expect, log that no sequences exist and return a blank array.
-		if ( ! is_array( $response['courses'] ) ) {
-			$this->log( 'API: get_sequences(): Error: No sequences exist in ConvertKit.' );
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'response_type_unexpected' ) );
-		}
-
-		// If no sequences exist, log that no sequences exist and return a blank array.
-		if ( ! count( $response['courses'] ) ) {
-			$this->log( 'API: get_sequences(): Error: No sequences exist in ConvertKit.' );
-			return $sequences;
-		}
-
-		foreach ( $response['courses'] as $sequence ) {
-			$sequences[ $sequence['id'] ] = $sequence;
-		}
-
-		return $sequences;
-
-	}
-
-	/**
-	 * Subscribes an email address to a sequence.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int    $sequence_id Sequence ID.
-	 * @param   string $email       Email Address.
-	 * @param   string $first_name  First Name.
-	 * @param   mixed  $fields      Custom Fields (false|array).
-	 * @return  WP_Error|array
-	 */
-	public function sequence_subscribe( $sequence_id, $email, $first_name = '', $fields = false ) {
-
-		$this->log( 'API: sequence_subscribe(): [ sequence_id: ' . $sequence_id . ', email: ' . $email . ']' );
-
-		// Sanitize some parameters.
-		$sequence_id = absint( $sequence_id );
-		$email       = trim( $email );
-		$first_name  = trim( $first_name );
-
-		// Return error if no Sequence ID or email address is specified.
-		if ( empty( $sequence_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'sequence_subscribe_sequence_id_empty' ) );
-		}
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'sequence_subscribe_email_empty' ) );
-		}
-
-		// Build request parameters.
-		$params = array(
-			'api_key'    => $this->api_key,
-			'email'      => $email,
-			'first_name' => $first_name,
-		);
-		if ( $fields ) {
-			$params['fields'] = $fields;
-		}
-
-		// Send request.
-		$response = $this->post( 'sequences/' . $sequence_id . '/subscribe', $params );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: sequence_subscribe(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully subscribed to the sequence.
-		 *
-		 * @since   1.0.0
-		 *
-		 * @param   array   $response       API Response
-		 * @param   int     $sequence_id    Sequence ID
-		 * @param   string  $email          Email Address
-		 * @param   mixed   $fields         Custom Fields (false|array)
-		 */
-		do_action( 'convertkit_api_sequence_subscribe_success', $response, $sequence_id, $email, $fields );
-
-		return $response;
-
-	}
-
-	/**
-	 * Fetches all tags from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function get_tags() {
-
-		$this->log( 'API: get_tags()' );
-
-		$tags = array();
-
-		// Send request.
-		$response = $this->get(
-			'tags',
-			array(
-				'api_key' => $this->api_key,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_tags(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		// If the response isn't an array as we expect, log that no tags exist and return a blank array.
-		if ( ! is_array( $response['tags'] ) ) {
-			$this->log( 'API: get_tags(): Error: No tags exist in ConvertKit.' );
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'response_type_unexpected' ) );
-		}
-
-		// If no tags exist, log that no tags exist and return a blank array.
-		if ( ! count( $response['tags'] ) ) {
-			$this->log( 'API: get_tags(): Error: No tags exist in ConvertKit.' );
-			return $tags;
-		}
-
-		foreach ( $response['tags'] as $tag ) {
-			$tags[ $tag['id'] ] = $tag;
-		}
-
-		return $tags;
-
-	}
-
-	/**
-	 * Subscribes an email address to a tag.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int    $tag_id     Tag ID.
-	 * @param   string $email      Email Address.
-	 * @param   string $first_name First Name.
-	 * @param   mixed  $fields     Custom Fields (false|array).
-	 * @return  WP_Error|array
-	 */
-	public function tag_subscribe( $tag_id, $email, $first_name = '', $fields = false ) {
-
-		$this->log( 'API: tag_subscribe(): [ tag_id: ' . $tag_id . ', email: ' . $email . ']' );
-
-		// Sanitize some parameters.
-		$tag_id     = absint( $tag_id );
-		$email      = trim( $email );
-		$first_name = trim( $first_name );
-
-		// Return error if no Tag ID or email address is specified.
-		if ( empty( $tag_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'tag_subscribe_tag_id_empty' ) );
-		}
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'tag_subscribe_email_empty' ) );
-		}
-
-		// Build request parameters.
-		$params = array(
-			'api_key'    => $this->api_key,
-			'email'      => $email,
-			'first_name' => $first_name,
-		);
-		if ( $fields ) {
-			$params['fields'] = $fields;
-		}
-
-		// Send request.
-		$response = $this->post( 'tags/' . $tag_id . '/subscribe', $params );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: tag_subscribe(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully subscribed to the tag.
-		 *
-		 * @since   1.0.0
-		 *
-		 * @param   array   $response   API Response
-		 * @param   int     $tag_id     Tag ID
-		 * @param   string  $email      Email Address
-		 * @param   mixed   $fields     Custom Fields (false|array).
-		 */
-		do_action( 'convertkit_api_tag_subscribe_success', $response, $tag_id, $email, $fields );
-
-		return $response;
-
-	}
-
-	/**
-	 * Removes a tag from the subscriber by their email address.
-	 *
-	 * @since   1.4.0
-	 *
-	 * @param   int    $tag_id     Tag ID.
-	 * @param   string $email      Email Address.
-	 * @return  WP_Error|array
-	 */
-	public function tag_unsubscribe( $tag_id, $email ) {
-
-		$this->log( 'API: tag_unsubscribe(): [ tag_id: ' . $tag_id . ', email: ' . $email . ']' );
-
-		// Sanitize some parameters.
-		$tag_id = absint( $tag_id );
-		$email  = trim( $email );
-
-		// Return error if no Tag ID or email address is specified.
-		if ( empty( $tag_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'tag_unsubscribe_tag_id_empty' ) );
-		}
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'tag_unsubscribe_email_empty' ) );
-		}
-
-		// Return error if an invalid email is specified.
-		// Passing an invalid email to the API doesn't return an error, so we need to check here.
-		if ( ! filter_var( $email, FILTER_VALIDATE_EMAIL ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'tag_unsubscribe_email_invalid' ) );
-		}
-
-		// Build request parameters.
-		$params = array(
-			'api_secret' => $this->api_secret,
-			'email'      => $email,
-		);
-
-		// Send request.
-		$response = $this->post( 'tags/' . $tag_id . '/unsubscribe', $params );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: tag_unsubscribe(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully unsubscribed from the tag.
-		 *
-		 * @since   1.4.0
-		 *
-		 * @param   array   $response   API Response
-		 * @param   int     $tag_id     Tag ID
-		 * @param   string  $email      Email Address
-		 */
-		do_action( 'convertkit_api_tag_unsubscribe_success', $response, $tag_id, $email );
-
-		return $response;
-
-	}
-
-	/**
-	 * Gets a subscriber by their email address.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $email  Email Address.
-	 * @return  WP_Error|array
-	 */
-	public function get_subscriber_by_email( $email ) {
-
-		$this->log( 'API: get_subscriber_by_email(): [ email: ' . $email . ']' );
-
-		// Sanitize some parameters.
-		$email = trim( $email );
-
-		// Return error if email address is specified.
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'get_subscriber_by_email_email_empty' ) );
-		}
-
-		// Send request.
-		$response = $this->get(
-			'subscribers',
-			array(
-				'api_secret'    => $this->api_secret,
-				'email_address' => $email,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_subscriber_by_email(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		// If no matching subscribers exist, log that no matching subscribers exist and return a blank array.
-		if ( (int) $response['total_subscribers'] === 0 ) {
-			$error = new WP_Error(
-				'convertkit_api_error',
-				sprintf(
-					$this->get_error_message( 'get_subscriber_by_email_none' ),
-					$email
-				)
-			);
-
-			$this->log( 'API: get_subscriber_by_email(): Error: ' . $error->get_error_message() );
-			return $error;
-		}
-
-		// Return subscriber.
-		return $response['subscribers'][0];
-
-	}
-
-	/**
-	 * Gets a subscriber by their ConvertKit subscriber ID.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int $subscriber_id  Subscriber ID.
-	 * @return  WP_Error|array
-	 */
-	public function get_subscriber_by_id( $subscriber_id ) {
-
-		$this->log( 'API: get_subscriber_by_id(): [ subscriber_id: ' . $subscriber_id . ']' );
-
-		// Sanitize some parameters.
-		$subscriber_id = absint( $subscriber_id );
-
-		// Return error if no Subscriber ID is specified.
-		if ( empty( $subscriber_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'get_subscriber_by_id_subscriber_id_empty' ) );
-		}
-
-		// Send request.
-		$response = $this->get(
-			'subscribers/' . $subscriber_id,
-			array(
-				'api_secret' => $this->api_secret,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_subscriber_by_id(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		return $response['subscriber'];
-
-	}
-
-	/**
-	 * Gets a list of tags for the given ConvertKit subscriber ID.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int $subscriber_id  Subscriber ID.
-	 * @return  WP_Error|array
-	 */
-	public function get_subscriber_tags( $subscriber_id ) {
-
-		$this->log( 'API: get_subscriber_tags(): [ subscriber_id: ' . $subscriber_id . ']' );
-
-		// Sanitize some parameters.
-		$subscriber_id = absint( $subscriber_id );
-
-		// Return error if no Subscriber ID is specified.
-		if ( empty( $subscriber_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'get_subscriber_tags_subscriber_id_empty' ) );
-		}
-
-		// Send request.
-		$response = $this->get(
-			'subscribers/' . $subscriber_id . '/tags',
-			array(
-				'api_key' => $this->api_key,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_subscriber_tags(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		return $response['tags'];
-
-	}
-
-	/**
-	 * Returns the subscriber's ID by their email address.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $email_address  Email Address.
-	 * @return  WP_Error|int
-	 */
-	public function get_subscriber_id( $email_address ) {
-
-		// Get subscriber.
-		$subscriber = $this->get_subscriber_by_email( $email_address );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $subscriber ) ) {
-			return $subscriber;
-		}
-
-		// Return ID.
-		return $subscriber['id'];
-
-	}
-
-	/**
-	 * Unsubscribes an email address.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $email      Email Address.
-	 * @return  WP_Error|array
-	 */
-	public function unsubscribe( $email ) {
-
-		$this->log( 'API: unsubscribe(): [ email: ' . $email . ']' );
-
-		// Sanitize some parameters.
-		$email = trim( $email );
-
-		// Return error if no email address is specified.
-		if ( empty( $email ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'unsubscribe_email_empty' ) );
-		}
-
-		// Send request.
-		$response = $this->put(
-			'unsubscribe',
-			array(
-				'api_secret' => $this->api_secret,
-				'email'      => $email,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: unsubscribe(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully unsubscribed.
-		 *
-		 * @since   1.0.0
-		 *
-		 * @param   array   $response   API Response
-		 * @param   string  $email      Email Address
-		 */
-		do_action( 'convertkit_api_form_unsubscribe_success', $response, $email );
-
-		return $response;
-
-	}
-
-	/**
-	 * Creates a broadcast.
-	 *
-	 * @since   1.3.9
-	 *
-	 * @param string    $subject               The broadcast email's subject.
-	 * @param string    $content               The broadcast's email HTML content.
-	 * @param string    $description           An internal description of this broadcast.
-	 * @param boolean   $is_public             Specifies whether or not this is a public post.
-	 * @param \DateTime $published_at          Specifies the time that this post was published (applicable
-	 *                                         only to public posts).
-	 * @param \DateTime $send_at               Time that this broadcast should be sent; leave blank to create
-	 *                                         a draft broadcast. If set to a future time, this is the time that
-	 *                                         the broadcast will be scheduled to send.
-	 * @param string    $email_address         Sending email address; leave blank to use your account's
-	 *                                         default sending email address.
-	 * @param string    $email_layout_template Name of the email template to use; leave blank to use your
-	 *                                         account's default email template.
-	 * @param string    $thumbnail_alt         Specify the ALT attribute of the public thumbnail image
-	 *                                         (applicable only to public posts).
-	 * @param string    $thumbnail_url         Specify the URL of the thumbnail image to accompany the broadcast
-	 *                                         post (applicable only to public posts).
-	 *
-	 * @see https://developers.convertkit.com/#create-a-broadcast
-	 *
-	 * @return WP_Error|array
-	 */
-	public function broadcast_create(
-		string $subject = '',
-		string $content = '',
-		string $description = '',
-		bool $is_public = false,
-		\DateTime $published_at = null,
-		\DateTime $send_at = null,
-		string $email_address = '',
-		string $email_layout_template = '',
-		string $thumbnail_alt = '',
-		string $thumbnail_url = ''
-	) {
-
-		$this->log( 'API: broadcast_create(): [ subject: ' . $subject . ']' );
-
-		// Build request parameters.
-		$params = array(
-			'api_secret'            => $this->api_secret,
-			'content'               => $content,
-			'description'           => $description,
-			'email_address'         => $email_address,
-			'email_layout_template' => $email_layout_template,
-			'public'                => $is_public,
-			'published_at'          => ( ! is_null( $published_at ) ? $published_at->format( 'Y-m-d H:i:s' ) : '' ),
-			'send_at'               => ( ! is_null( $send_at ) ? $send_at->format( 'Y-m-d H:i:s' ) : '' ),
-			'subject'               => $subject,
-			'thumbnail_alt'         => $thumbnail_alt,
-			'thumbnail_url'         => $thumbnail_url,
-		);
-
-		// Iterate through parameters, removing blank entries.
-		foreach ( $params as $key => $value ) {
-			if ( is_string( $value ) && strlen( $value ) === 0 ) {
-				unset( $params[ $key ] );
-			}
-		}
-
-		// If the post isn't public, remove some params that don't apply.
-		if ( ! $is_public ) {
-			unset( $params['published_at'], $params['thumbnail_alt'], $params['thumbnail_url'] );
-		}
-
-		// Send request.
-		$response = $this->post( 'broadcasts', $params );
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: broadcast_create(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		/**
-		 * Runs actions immediately after the email address was successfully subscribed to the tag.
-		 *
-		 * @since   1.3.9
-		 *
-		 * @param   array   $response   API Response.
-		 * @param   array   $params     Request parameters.
-		 */
-		do_action( 'convertkit_api_broadcast_create_success', $response, $params );
-
-		// Return broadcast.
-		return $response['broadcast'];
-
-	}
-
-	/**
-	 * Deletes a Broadcast.
-	 *
-	 * @since   1.3.9
-	 *
-	 * @param   int $broadcast_id   Broadcast ID.
-	 * @return  WP_Error|null
-	 */
-	public function broadcast_delete( $broadcast_id ) {
-
-		$this->log( 'API: broadcast_delete(): [ broadcast_id: ' . $broadcast_id . ']' );
-
-		// Sanitize some parameters.
-		$broadcast_id = absint( $broadcast_id );
-
-		// Return error if no Broadcast ID is specified.
-		if ( empty( $broadcast_id ) ) {
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'broadcast_delete_broadcast_id_empty' ) );
-		}
+	 */
+	public function refresh_token() {
 
-		// Build request parameters.
-		$params = array(
-			'api_secret' => $this->api_secret,
+		$result = $this->post(
+			'token',
+			array(
+				'client_id'     => $this->client_id,
+				'grant_type'    => 'refresh_token',
+				'refresh_token' => $this->refresh_token,
+			)
 		);
 
-		// Send request.
-		$response = $this->delete( 'broadcasts/' . $broadcast_id, $params );
-
 		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: broadcast_delete(): Error: ' . $response->get_error_message() );
-			return $response;
+		if ( is_wp_error( $result ) ) {
+			$this->log( 'API: Error: ' . $result->get_error_message() );
+			return $result;
 		}
 
+		// Update the access and refresh tokens in this class.
+		$this->access_token  = $result['access_token'];
+		$this->refresh_token = $result['refresh_token'];
+
 		/**
-		 * Runs actions immediately after the broadcast was deleted.
+		 * Perform any actions with the new access token, such as saving it.
 		 *
-		 * @since   1.0.0
+		 * @since   2.0.0
 		 *
-		 * @param   null|array   $response       API Response
-		 * @param   int          $broadcast_id   Broadcast ID
+		 * @param   array   $result     Access Token, Refresh Token, Expiry, Bearer and Scope.
+		 * @param   string  $client_id  OAUth Client ID.
 		 */
-		do_action( 'convertkit_api_broadcast_delete_success', $response, $broadcast_id );
+		do_action( 'convertkit_api_refresh_token', $result, $this->client_id );
 
-		// Response will be null if successful.
-		return $response;
+		// Return.
+		return $result;
 
 	}
 
 	/**
-	 * Gets all custom fields from the API.
+	 * Exchanges the given API Key for an Access Token.
 	 *
-	 * @since   1.0.0
+	 * @since   2.0.0
 	 *
+	 * @param   string $api_key    API Key.
+	 * @param   string $api_secret API Secret.
 	 * @return  WP_Error|array
 	 */
-	public function get_custom_fields() {
-
-		$this->log( 'API: get_custom_fields()' );
+	public function exchange_api_key_and_secret_for_access_token( $api_key, $api_secret ) {
 
-		$custom_fields = array();
-
-		// Send request.
-		$response = $this->get(
-			'custom_fields',
+		return $this->post(
+			'accounts/oauth_access_token',
 			array(
-				'api_key' => $this->api_key,
+				'api_key'    => $api_key,
+				'api_secret' => $api_secret,
 			)
 		);
 
-		// If an error occured, return WP_Error.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_custom_fields(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		// If the response isn't an array as we expect, log that no tags exist and return a blank array.
-		if ( ! is_array( $response['custom_fields'] ) ) {
-			$this->log( 'API: get_custom_fields(): Error: No custom fields exist in ConvertKit.' );
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'response_type_unexpected' ) );
-		}
-
-		// If no custom fields exist, log that no custom fields exist and return a blank array.
-		if ( ! count( $response['custom_fields'] ) ) {
-			$this->log( 'API: get_custom_fields(): Error: No custom fields exist in ConvertKit.' );
-			return $custom_fields;
-		}
-
-		foreach ( $response['custom_fields'] as $custom_field ) {
-			$custom_fields[ $custom_field['id'] ] = $custom_field;
-		}
-
-		return $custom_fields;
-
 	}
 
 	/**
@@ -1411,10 +558,8 @@ public function get_posts( $page = 1, $per_page = 10 ) {
 		$response = $this->get(
 			'posts',
 			array(
-				'api_key'    => $this->api_key,
-				'api_secret' => $this->api_secret,
-				'page'       => $page,
-				'per_page'   => $per_page,
+				'page'     => $page,
+				'per_page' => $per_page,
 			)
 		);
 
@@ -1455,9 +600,6 @@ public function get_post( $post_id ) {
 		// Send request.
 		$response = $this->get(
 			sprintf( 'posts/%s', $post_id ),
-			array(
-				'api_secret' => $this->api_secret,
-			)
 		);
 
 		// If an error occured, return WP_Error.
@@ -1491,42 +633,7 @@ public function get_post( $post_id ) {
 	 */
 	public function get_products() {
 
-		$this->log( 'API: get_products()' );
-
-		$products = array();
-
-		// Send request.
-		$response = $this->get(
-			'products',
-			array(
-				'api_key'    => $this->api_key,
-				'api_secret' => $this->api_secret,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: get_products(): Error: ' . $response->get_error_message() );
-			return $response;
-		}
-
-		// If the response isn't an array as we expect, log that no products exist and return a blank array.
-		if ( ! is_array( $response['products'] ) ) {
-			$this->log( 'API: get_products(): Error: No products exist in ConvertKit.' );
-			return new WP_Error( 'convertkit_api_error', $this->get_error_message( 'response_type_unexpected' ) );
-		}
-
-		// If no products exist, log that no products exist and return a blank array.
-		if ( ! count( $response['products'] ) ) {
-			$this->log( 'API: get_products(): Error: No products exist in ConvertKit.' );
-			return $products;
-		}
-
-		foreach ( $response['products'] as $product ) {
-			$products[ $product['id'] ] = $product;
-		}
-
-		return $products;
+		return $this->get( 'products' );
 
 	}
 
@@ -1568,8 +675,6 @@ public function subscriber_authentication_send_code( $email, $redirect_url ) {
 		$response = $this->post(
 			'subscriber_authentication/send_code',
 			array(
-				'api_key'       => $this->api_key,
-				'api_secret'    => $this->api_secret,
 				'email_address' => $email,
 				'redirect_url'  => $redirect_url,
 			)
@@ -1622,8 +727,6 @@ public function subscriber_authentication_verify( $token, $subscriber_code ) {
 		$response = $this->post(
 			'subscriber_authentication/verify',
 			array(
-				'api_key'         => $this->api_key,
-				'api_secret'      => $this->api_secret,
 				'token'           => $token,
 				'subscriber_code' => $subscriber_code,
 			)
@@ -1670,11 +773,7 @@ public function profile( $signed_subscriber_id ) {
 
 		// Send request.
 		$response = $this->get(
-			'profile/' . $signed_subscriber_id,
-			array(
-				'api_key'    => $this->api_key,
-				'api_secret' => $this->api_secret,
-			)
+			'profile/' . $signed_subscriber_id
 		);
 
 		// If an error occured, log and return it now.
@@ -1775,138 +874,6 @@ public function get_landing_page_html( $url, $debug = false ) {
 
 	}
 
-	/**
-	 * Create a Purchase.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   array $purchase   Purchase Data.
-	 * @return  WP_Error|array
-	 */
-	public function purchase_create( $purchase ) {
-
-		$this->log( 'API: purchase_create(): [ purchase: ' . print_r( $purchase, true ) . ']' ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions
-
-		$response = $this->post(
-			'purchases',
-			array(
-				'api_secret' => $this->api_secret,
-				'purchase'   => $purchase,
-			)
-		);
-
-		if ( is_wp_error( $response ) ) {
-			$this->log( 'API: purchase_create(): Error: ' . $response->get_error_message() );
-		}
-
-		/**
-		 * Runs actions immediately after the purchase data address was successfully created.
-		 *
-		 * @since   1.0.0
-		 *
-		 * @param   array   $response   API Response
-		 * @param   array   $purchase   Purchase Data
-		 */
-		do_action( 'convertkit_api_purchase_create_success', $response, $purchase );
-
-		return $response;
-
-	}
-
-	/**
-	 * Returns the recommendations script URL for this account from the API,
-	 * used to display the Creator Network modal when a form is submitted.
-	 *
-	 * @since   1.3.7
-	 *
-	 * @return  WP_Error|array
-	 */
-	public function recommendations_script() {
-
-		$this->log( 'API: recommendations_script()' );
-
-		return $this->get(
-			'recommendations_script',
-			array(
-				'api_secret' => $this->api_secret,
-			)
-		);
-
-	}
-
-	/**
-	 * Backward compat. function for getting a ConvertKit subscriber by their ID.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int $id     Subscriber ID.
-	 * @return  WP_Error|array
-	 */
-	public function get_subscriber( $id ) {
-
-		// Warn the developer that they shouldn't use this function.
-		_deprecated_function( __FUNCTION__, '1.0.0', 'get_subscriber_by_id()' );
-
-		// Pass request to new function.
-		return $this->get_subscriber_by_id( $id );
-
-	}
-
-	/**
-	 * Backward compat. function for subscribing a ConvertKit subscriber to the given Tag.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   int   $tag    Tag ID.
-	 * @param   array $args   Arguments.
-	 * @return  WP_Error|array
-	 */
-	public function add_tag( $tag, $args ) {
-
-		// Warn the developer that they shouldn't use this function.
-		_deprecated_function( __FUNCTION__, '1.0.0', 'tag_subscribe( $tag_id, $email_address )' );
-
-		// Pass request to new function.
-		return $this->tag_subscribe( $tag, $args['email'] );
-
-	}
-
-	/**
-	 * Backward compat. function for fetching Legacy Form or Landing Page markup for the given URL.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $url    URL.
-	 * @return  WP_Error|string
-	 */
-	public function get_resource( $url ) {
-
-		// Warn the developer that they shouldn't use this function.
-		_deprecated_function( __FUNCTION__, '1.0.0', 'get_form_html( $form_id ) or get_landing_page_html( $url )' );
-
-		// Pass request to new function.
-		return $this->get_landing_page_html( $url );
-
-	}
-
-	/**
-	 * Backward compat. function for fetching Legacy Form or Landing Page markup for the given URL.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   array $args   Arguments (single email key).
-	 * @return  WP_Error|array
-	 */
-	public function form_unsubscribe( $args ) {
-
-		// Warn the developer that they shouldn't use this function.
-		_deprecated_function( __FUNCTION__, '1.0.0', 'unsubscribe( $email_address )' );
-
-		// Pass request to new function.
-		return $this->unsubscribe( $args['email'] );
-
-	}
-
 	/**
 	 * Adds the given entry to the log file, if debugging is enabled.
 	 *
@@ -2035,174 +1002,6 @@ private function is_json( $json_string ) {
 
 	}
 
-	/**
-	 * Converts any relative URls to absolute, fully qualified HTTP(s) URLs for the given
-	 * DOM Elements.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   DOMNodeList<DOMElement> $elements   Elements.
-	 * @param   string                  $attribute  HTML Attribute.
-	 * @param   string                  $url        Absolute URL to prepend to relative URLs.
-	 */
-	private function convert_relative_to_absolute_urls( $elements, $attribute, $url ) {
-
-		// Anchor hrefs.
-		foreach ( $elements as $element ) {
-			// Skip if the attribute's value is empty.
-			if ( empty( $element->getAttribute( $attribute ) ) ) {
-				continue;
-			}
-
-			// Skip if the attribute's value is a fully qualified URL.
-			if ( filter_var( $element->getAttribute( $attribute ), FILTER_VALIDATE_URL ) ) {
-				continue;
-			}
-
-			// Skip if this is a Google Font CSS URL.
-			if ( strpos( $element->getAttribute( $attribute ), '//fonts.googleapis.com' ) !== false ) {
-				continue;
-			}
-
-			// If here, the attribute's value is a relative URL, missing the http(s) and domain.
-			// Prepend the URL to the attribute's value.
-			$element->setAttribute( $attribute, $url . $element->getAttribute( $attribute ) );
-		}
-
-	}
-
-	/**
-	 * Strips <html>, <head> and <body> opening and closing tags from the given markup,
-	 * as well as the Content-Type meta tag we might have added in get_html().
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $markup     HTML Markup.
-	 * @return  string              HTML Markup
-	 * */
-	private function strip_html_head_body_tags( $markup ) {
-
-		$markup = str_replace( '<html>', '', $markup );
-		$markup = str_replace( '</html>', '', $markup );
-		$markup = str_replace( '<head>', '', $markup );
-		$markup = str_replace( '</head>', '', $markup );
-		$markup = str_replace( '<body>', '', $markup );
-		$markup = str_replace( '</body>', '', $markup );
-		$markup = str_replace( '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">', '', $markup );
-
-		return $markup;
-
-	}
-
-	/**
-	 * Gets all forms and landing pages from the API.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @return  WP_Error|array
-	 */
-	private function get_forms_landing_pages() {
-
-		// Send request.
-		$response = $this->get(
-			'forms',
-			array(
-				'api_key' => $this->api_key,
-			)
-		);
-
-		// If an error occured, log and return it now.
-		if ( is_wp_error( $response ) ) {
-			return $response;
-		}
-
-		// Iterate through forms, determining if each form is a form or landing page.
-		$forms         = array();
-		$landing_pages = array();
-		foreach ( $response['forms'] as $form ) {
-			// Skip archived forms.
-			if ( isset( $form['archived'] ) && $form['archived'] ) {
-				continue;
-			}
-
-			switch ( $form['type'] ) {
-				case 'hosted':
-					$landing_pages[ $form['id'] ] = $form;
-					break;
-
-				default:
-					$forms[ $form['id'] ] = $form;
-					break;
-			}
-		}
-
-		return array(
-			'forms'         => $forms,
-			'landing_pages' => $landing_pages,
-		);
-
-	}
-
-	/**
-	 * Performs a GET request.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $endpoint       API Endpoint.
-	 * @param   array  $params         Params.
-	 * @return  WP_Error|array|null
-	 */
-	private function get( $endpoint, $params = array() ) {
-
-		return $this->request( $endpoint, 'get', $params, true );
-
-	}
-
-	/**
-	 * Performs a POST request.
-	 *
-	 * @since  1.0.0
-	 *
-	 * @param   string $endpoint       API Endpoint.
-	 * @param   array  $params         Params.
-	 * @return  WP_Error|array|null
-	 */
-	private function post( $endpoint, $params = array() ) {
-
-		return $this->request( $endpoint, 'post', $params, true );
-
-	}
-
-	/**
-	 * Performs a PUT request.
-	 *
-	 * @since  1.0.0
-	 *
-	 * @param   string $endpoint       API Endpoint.
-	 * @param   array  $params         Params.
-	 * @return  WP_Error|array|null
-	 */
-	private function put( $endpoint, $params = array() ) {
-
-		return $this->request( $endpoint, 'put', $params, true );
-
-	}
-
-	/**
-	 * Performs a DELETE request.
-	 *
-	 * @since  1.3.9
-	 *
-	 * @param   string $endpoint       API Endpoint.
-	 * @param   array  $params         Params.
-	 * @return  WP_Error|null
-	 */
-	private function delete( $endpoint, $params = array() ) {
-
-		return $this->request( $endpoint, 'delete', $params, true );
-
-	}
-
 	/**
 	 * Main function which handles sending requests to the API using WordPress functions.
 	 *
@@ -2214,16 +1013,17 @@ private function delete( $endpoint, $params = array() ) {
 	 * @param   bool   $retry_if_rate_limit_hit Retry request if rate limit hit.
 	 * @return  WP_Error|array|null
 	 */
-	private function request( $endpoint, $method = 'get', $params = array(), $retry_if_rate_limit_hit = true ) {
+	public function request( $endpoint, $method = 'get', $params = array(), $retry_if_rate_limit_hit = true ) {
 
 		// Send request.
-		switch ( $method ) {
+		switch ( strtolower( $method ) ) {
 			case 'get':
+				// We deliberate don't use add_query_arg(), as this converts double equal signs (typically
+				// provided by `start_cursor` and `end_cursor`) to a single equal sign, therefore breaking
+				// pagination.  http_build_query() will encode equals signs instead, preserving them
+				// and ensuring paginated requests work correctly.
 				$result = wp_remote_get(
-					$this->add_params_to_url(
-						$this->get_api_url( $endpoint ),
-						$params
-					),
+					$this->get_api_url( $endpoint ) . '?' . http_build_query( $params ),
 					array(
 						'headers'    => $this->get_request_headers(),
 						'timeout'    => $this->get_timeout(),
@@ -2345,6 +1145,13 @@ private function request( $endpoint, $method = 'get', $params = array(), $retry_
 				$error = implode( "\n", $response['errors'] );
 			} elseif ( array_key_exists( 'error_description', $response ) ) {
 				$error = $response['error_description'];
+			} elseif ( array_key_exists( 'error', $response ) ) {
+				// The 'error' key is present when exchanging an API Key and Secret for an Access Token
+				// and something went wrong e.g. invalid API credentials.
+				$error = $response['error'];
+				if ( array_key_exists( 'message', $response ) ) {
+					$error .= ': ' . $response['message'];
+				}
 			}
 
 			$this->log( 'API: Error: ' . $error );
@@ -2513,26 +1320,11 @@ private function get_api_url( $endpoint ) {
 			}
 		}
 
-		// For all other endpoints, it's https://api.convertkit.com/v3/$endpoint.
+		// For all other endpoints, it's https://api.convertkit.com/v4/$endpoint.
 		return path_join( $this->api_url_base . $this->api_version, $endpoint );
 
 	}
 
-	/**
-	 * Adds the supplied array of parameters as query arguments to the URL.
-	 *
-	 * @since   1.0.0
-	 *
-	 * @param   string $url        URL.
-	 * @param   array  $params     Parameters for request.
-	 * @return  string              URL with API Key or API Secret
-	 */
-	private function add_params_to_url( $url, $params ) {
-
-		return add_query_arg( $params, $url );
-
-	}
-
 	/**
 	 * Returns the localized/translated error message for the given error key.
 	 *
diff --git a/src/class-convertkit-resource.php b/src/class-convertkit-resource.php
index 41adf69..d076dab 100644
--- a/src/class-convertkit-resource.php
+++ b/src/class-convertkit-resource.php
@@ -356,23 +356,11 @@ public function refresh() {
 		// Fetch resources.
 		switch ( $this->type ) {
 			case 'forms':
-				$results = $this->api->get_forms();
-				break;
-
 			case 'landing_pages':
-				$results = $this->api->get_landing_pages();
-				break;
-
 			case 'tags':
-				$results = $this->api->get_tags();
-				break;
-
 			case 'sequences':
-				$results = $this->api->get_sequences();
-				break;
-
 			case 'custom_fields':
-				$results = $this->api->get_custom_fields();
+				$results = $this->get_all_resources( $this->type );
 				break;
 
 			case 'posts':
@@ -381,6 +369,11 @@ public function refresh() {
 
 			case 'products':
 				$results = $this->api->get_products();
+				if ( is_wp_error( $results ) ) {
+					return $results;
+				}
+
+				$results = $this->map( $results, array(), 'products' );
 				break;
 
 			default:
@@ -508,4 +501,94 @@ public function delete() {
 
 	}
 
+	/**
+	 * Fetches all resources (forms, landing pages, tags etc) from the API,
+	 * using cursor pagination until all results are returned.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @param   string $resource_type   Resource (forms,landing_pages,tags,sequences,custom_fields).
+	 * @param   int    $per_page        Number of results to return per request.
+	 */
+	private function get_all_resources( $resource_type, $per_page = 100 ) {
+
+		// Fetch resources.
+		$response = call_user_func_array(
+			array( $this->api, 'get_' . $resource_type ),
+			array(
+				'active',
+				false,
+				'',
+				'',
+				$per_page,
+			)
+		);
+
+		// Bail if an error occured.
+		if ( is_wp_error( $response ) ) {
+			return $response;
+		}
+
+		// Append resources to array.
+		$items = $this->map( $response, array(), $resource_type );
+
+		// If no further resources to fetch, return.
+		if ( ! $response['pagination']['has_next_page'] ) {
+			return $items;
+		}
+
+		// Further resources need to be fetched.
+		while ( $response['pagination']['has_next_page'] ) {
+			// Fetch next page of resources.
+			$response = call_user_func_array(
+				array(
+					$this->api,
+					'get_' . $resource_type,
+				),
+				array(
+					'active',
+					false,
+					$response['pagination']['end_cursor'],
+					'',
+					$per_page,
+				)
+			);
+
+			// Bail if an error occured.
+			if ( is_wp_error( $response ) ) {
+				return $response;
+			}
+
+			// Append resources to array.
+			$items = $this->map( $response, $items, $resource_type );
+		}
+
+		return $items;
+
+	}
+
+	/**
+	 * Helper method to build an array of resources with keys as IDs.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @param   array  $response        API Response.
+	 * @param   array  $items           Key'd resources.
+	 * @param   string $resource_type   Resource (forms,landing_pages,tags,sequences,custom_fields).
+	 */
+	private function map( $response, $items = array(), $resource_type = 'forms' ) {
+
+		// If we're building an array of landing pages, use the `form` key.
+		if ( $resource_type === 'landing_pages' ) {
+			$resource_type = 'forms';
+		}
+
+		foreach ( $response[ $resource_type ] as $item ) {
+			$items[ $item['id'] ] = $item;
+		}
+
+		return $items;
+
+	}
+
 }
diff --git a/tests/wpunit/APITest.php b/tests/wpunit/APITest.php
index 49f0f06..936a561 100644
--- a/tests/wpunit/APITest.php
+++ b/tests/wpunit/APITest.php
@@ -31,6 +31,15 @@ class APITest extends \Codeception\TestCase\WPTestCase
 	 */
 	private $errorCode = 'convertkit_api_error';
 
+	/**
+	 * Broadcast IDs to delete on teardown of a test.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @var     array<int, int>
+	 */
+	protected $broadcast_ids = [];
+
 	/**
 	 * Performs actions before each test.
 	 *
@@ -41,16 +50,18 @@ public function setUp(): void
 		parent::setUp();
 
 		// Include class from /src to test.
+		require_once 'src/class-convertkit-api-traits.php';
 		require_once 'src/class-convertkit-api.php';
 		require_once 'src/class-convertkit-log.php';
 
 		// Initialize the classes we want to test.
-		$this->api         = new ConvertKit_API(
+		$this->api = new ConvertKit_API(
 			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
 			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
 			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
 			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
 		);
+
 		$this->api_no_data = new ConvertKit_API(
 			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
 			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
@@ -66,6 +77,11 @@ public function setUp(): void
 	 */
 	public function tearDown(): void
 	{
+		// Delete any Broadcasts.
+		foreach ($this->broadcast_ids as $id) {
+			$this->api->delete_broadcast($id);
+		}
+
 		// Destroy the classes we tested.
 		unset($this->api);
 		unset($this->api_no_data);
@@ -138,7 +154,7 @@ public function test401Unauthorized()
 			'not-a-real-access-token',
 			'not-a-real-refresh-token'
 		);
-		$result = $api->account();
+		$result = $api->get_account();
 		$this->assertInstanceOf(WP_Error::class, $result);
 		$this->assertEquals($result->get_error_code(), $this->errorCode);
 		$this->assertEquals($result->get_error_message(), 'The access token is invalid');
@@ -164,7 +180,7 @@ public function test429RateLimitHit()
 				)
 			)
 		);
-		$result = $this->api->account(); // The API function we use doesn't matter, as mockResponse forces a 429 error.
+		$result = $this->api->get_account(); // The API function we use doesn't matter, as mockResponse forces a 429 error.
 		$this->assertInstanceOf(WP_Error::class, $result);
 		$this->assertEquals($result->get_error_code(), $this->errorCode);
 		$this->assertEquals($result->get_error_message(), 'ConvertKit API Error: Rate limit hit.');
@@ -180,7 +196,7 @@ public function test500InternalServerError()
 	{
 		// Force WordPress HTTP classes and functions to return a 500 error.
 		$this->mockResponses( 500, 'Internal server error.' );
-		$result = $this->api->account(); // The API function we use doesn't matter, as mockResponse forces a 500 error.
+		$result = $this->api->get_account(); // The API function we use doesn't matter, as mockResponse forces a 500 error.
 		$this->assertInstanceOf(WP_Error::class, $result);
 		$this->assertEquals($result->get_error_code(), $this->errorCode);
 		$this->assertEquals($result->get_error_message(), 'ConvertKit API Error: Internal server error.');
@@ -196,7 +212,7 @@ public function test502BadGateway()
 	{
 		// Force WordPress HTTP classes and functions to return a 502 error.
 		$this->mockResponses( 502, 'Bad gateway.' );
-		$result = $this->api->account(); // The API function we use doesn't matter, as mockResponse forces a 502 error.
+		$result = $this->api->get_account(); // The API function we use doesn't matter, as mockResponse forces a 502 error.
 		$this->assertInstanceOf(WP_Error::class, $result);
 		$this->assertEquals($result->get_error_code(), $this->errorCode);
 		$this->assertEquals($result->get_error_message(), 'ConvertKit API Error: Bad gateway.');
@@ -231,7 +247,7 @@ function($args, $url) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParam
 			false,
 			'TestContext'
 		);
-		$result = $api->account();
+		$result = $api->get_account();
 	}
 
 	/**
@@ -254,7 +270,7 @@ function($args, $url) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParam
 		);
 
 		// Perform a request.
-		$result = $this->api->account();
+		$result = $this->api->get_account();
 	}
 
 	/**
@@ -390,30 +406,239 @@ public function testRefreshTokenWithInvalidToken()
 	public function testInvalidAPICredentials()
 	{
 		$api    = new ConvertKit_API( $_ENV['CONVERTKIT_OAUTH_CLIENT_ID'], $_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'] );
-		$result = $api->account();
+		$result = $api->get_account();
 		$this->assertInstanceOf(WP_Error::class, $result);
 		$this->assertEquals($result->get_error_code(), $this->errorCode);
 		$this->assertEquals($result->get_error_message(), 'The access token is invalid');
 	}
 
+	/**
+	 * Test that exchanging a valid API Key and Secret for an Access Token returns the expected data.
+	 *
+	 * @since   2.0.0
+	 */
+	public function testExchangeAPIKeyAndSecretForAccessToken()
+	{
+		$api    = new ConvertKit_API( $_ENV['CONVERTKIT_OAUTH_CLIENT_ID'], $_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'] );
+		$result = $api->exchange_api_key_and_secret_for_access_token(
+			$_ENV['CONVERTKIT_API_KEY'],
+			$_ENV['CONVERTKIT_API_SECRET']
+		);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('oauth', $result);
+		$this->assertArrayHasKey('access_token', $result['oauth']);
+		$this->assertArrayHasKey('refresh_token', $result['oauth']);
+		$this->assertArrayHasKey('expires_at', $result['oauth']);
+	}
+
+	/**
+	 * Test that exchanging an invalid API Key and Secret for an Access Token returns a WP_Error.
+	 *
+	 * @since   2.0.0
+	 */
+	public function testExchangeInvalidAPIKeyAndSecretForAccessToken()
+	{
+		$api    = new ConvertKit_API( $_ENV['CONVERTKIT_OAUTH_CLIENT_ID'], $_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'] );
+		$result = $api->exchange_api_key_and_secret_for_access_token(
+			'invalid-api-key',
+			'invalid-api-secret'
+		);
+		$this->assertInstanceOf(WP_Error::class, $result);
+		$this->assertEquals($result->get_error_code(), $this->errorCode);
+		$this->assertEquals('Authorization Failed: API Secret not valid', $result->get_error_message());
+	}
+
 	/**
 	 * Test that supplying valid API credentials to the API class returns the expected account information.
 	 *
 	 * @since   1.0.0
 	 */
-	public function testAccount()
+	public function testGetAccount()
 	{
-		$result = $this->api->account();
+		$result = $this->api->get_account();
 		$this->assertNotInstanceOf(WP_Error::class, $result);
 		$this->assertIsArray($result);
+
 		$this->assertArrayHasKey('user', $result);
 		$this->assertArrayHasKey('account', $result);
+
 		$this->assertArrayHasKey('name', $result['account']);
 		$this->assertArrayHasKey('plan_type', $result['account']);
 		$this->assertArrayHasKey('primary_email_address', $result['account']);
 		$this->assertEquals('wordpress@convertkit.com', $result['account']['primary_email_address']);
 	}
 
+	/**
+	 * Test that get_account_colors() returns the expected data.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetAccountColors()
+	{
+		$result = $this->api->get_account_colors();
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('colors', $result);
+		$this->assertIsArray($result['colors']);
+	}
+
+	/**
+	 * Test that update_account_colors() updates the account's colors.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testUpdateAccountColors()
+	{
+		$result = $this->api->update_account_colors(
+			[
+				'#111111',
+			]
+		);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('colors', $result);
+		$this->assertIsArray($result['colors']);
+		$this->assertEquals($result['colors'][0], '#111111');
+	}
+
+	/**
+	 * Test that get_creator_profile() returns the expected data.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetCreatorProfile()
+	{
+		$result = $this->api->get_creator_profile();
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('name', $result['profile']);
+		$this->assertArrayHasKey('byline', $result['profile']);
+		$this->assertArrayHasKey('bio', $result['profile']);
+		$this->assertArrayHasKey('image_url', $result['profile']);
+		$this->assertArrayHasKey('profile_url', $result['profile']);
+	}
+
+	/**
+	 * Test that get_email_stats() returns the expected data.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetEmailStats()
+	{
+		$result = $this->api->get_email_stats();
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('sent', $result['stats']);
+		$this->assertArrayHasKey('clicked', $result['stats']);
+		$this->assertArrayHasKey('opened', $result['stats']);
+		$this->assertArrayHasKey('email_stats_mode', $result['stats']);
+		$this->assertArrayHasKey('open_tracking_enabled', $result['stats']);
+		$this->assertArrayHasKey('click_tracking_enabled', $result['stats']);
+		$this->assertArrayHasKey('starting', $result['stats']);
+		$this->assertArrayHasKey('ending', $result['stats']);
+	}
+
+	/**
+	 * Test that get_growth_stats() returns the expected data.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetGrowthStats()
+	{
+		$result = $this->api->get_growth_stats();
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('cancellations', $result['stats']);
+		$this->assertArrayHasKey('net_new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('subscribers', $result['stats']);
+		$this->assertArrayHasKey('starting', $result['stats']);
+		$this->assertArrayHasKey('ending', $result['stats']);
+	}
+
+	/**
+	 * Test that get_growth_stats() returns the expected data
+	 * when a start date is specified.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetGrowthStatsWithStartDate()
+	{
+		// Define start and end dates.
+		$starting = new DateTime('now');
+		$starting->modify('-7 days');
+		$ending = new DateTime('now');
+
+		// Send request.
+		$result = $this->api->get_growth_stats($starting);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		// Confirm response object contains expected keys.
+		$this->assertArrayHasKey('cancellations', $result['stats']);
+		$this->assertArrayHasKey('net_new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('subscribers', $result['stats']);
+		$this->assertArrayHasKey('starting', $result['stats']);
+		$this->assertArrayHasKey('ending', $result['stats']);
+
+		// Assert start and end dates were honored.
+		$this->assertEquals($result['stats']['starting'], $starting->format('Y-m-d') . 'T00:00:00-04:00');
+		$this->assertEquals($result['stats']['ending'], $ending->format('Y-m-d') . 'T23:59:59-04:00');
+	}
+
+	/**
+	 * Test that get_growth_stats() returns the expected data
+	 * when an end date is specified.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetGrowthStatsWithEndDate()
+	{
+		// Define start and end dates.
+		$starting = new DateTime('now');
+		$starting->modify('-90 days');
+		$ending = new DateTime('now');
+		$ending->modify('-7 days');
+
+		// Send request.
+		$result = $this->api->get_growth_stats(null, $ending);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		// Confirm response object contains expected keys.
+		$this->assertArrayHasKey('cancellations', $result['stats']);
+		$this->assertArrayHasKey('net_new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('new_subscribers', $result['stats']);
+		$this->assertArrayHasKey('subscribers', $result['stats']);
+		$this->assertArrayHasKey('starting', $result['stats']);
+		$this->assertArrayHasKey('ending', $result['stats']);
+
+		// Assert start and end dates were honored.
+		$this->assertEquals($result['stats']['starting'], $starting->format('Y-m-d') . 'T00:00:00-04:00');
+		$this->assertEquals($result['stats']['ending'], $ending->format('Y-m-d') . 'T23:59:59-04:00');
+	}
+
 	/**
 	 * Test that the `get_subscription_forms()` function returns expected data.
 	 *
@@ -1275,60 +1500,136 @@ public function testUnsubscribeWithInvalidEmail()
 		$this->assertEquals('Not Found: The entity you were trying to find doesn\'t exist', $result->get_error_message());
 	}
 
+
 	/**
-	 * Test that broadcast_create() and broadcast_delete() works when valid parameters are specified.
+	 * Test that get_broadcasts() returns the expected data
+	 * when pagination parameters and per_page limits are specified.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetBroadcastsPagination()
+	{
+		// Return one broadcast.
+		$result = $this->api->get_broadcasts(false, '', '', 1);
+
+		// Assert broadcasts and pagination exist.
+		$this->assertDataExists($result, 'broadcasts');
+		$this->assertPaginationExists($result);
+
+		// Assert a single broadcast was returned.
+		$this->assertCount(1, $result['broadcasts']);
+
+		// Assert has_previous_page and has_next_page are correct.
+		$this->assertFalse($result['pagination']['has_previous_page']);
+		$this->assertTrue($result['pagination']['has_next_page']);
+
+		// Use pagination to fetch next page.
+		$result = $this->api->get_broadcasts(false, $result['pagination']['end_cursor'], '', 1);
+
+		// Assert broadcasts and pagination exist.
+		$this->assertDataExists($result, 'broadcasts');
+		$this->assertPaginationExists($result);
+
+		// Assert a single broadcast was returned.
+		$this->assertCount(1, $result['broadcasts']);
+
+		// Assert has_previous_page and has_next_page are correct.
+		$this->assertTrue($result['pagination']['has_previous_page']);
+		$this->assertTrue($result['pagination']['has_next_page']);
+
+		// Use pagination to fetch previous page.
+		$result = $this->api->get_broadcasts(false, '', $result['pagination']['start_cursor'], 1);
+
+		// Assert broadcasts and pagination exist.
+		$this->assertDataExists($result, 'broadcasts');
+		$this->assertPaginationExists($result);
+
+		// Assert a single broadcast was returned.
+		$this->assertCount(1, $result['broadcasts']);
+
+		// Assert has_previous_page and has_next_page are correct.
+		$this->assertFalse($result['pagination']['has_previous_page']);
+		$this->assertTrue($result['pagination']['has_next_page']);
+	}
+
+	/**
+	 * Test that create_broadcast(), update_broadcast() and delete_broadcast() works
+	 * when specifying valid published_at and send_at values.
 	 *
 	 * We do all tests in a single function, so we don't end up with unnecessary Broadcasts remaining
 	 * on the ConvertKit account when running tests, which might impact
 	 * other tests that expect (or do not expect) specific Broadcasts.
 	 *
-	 * @since   1.3.9
+	 * @since   2.0.0
+	 *
+	 * @return void
 	 */
-	public function testCreateAndDeleteDraftBroadcast()
+	public function testCreateUpdateAndDeleteDraftBroadcast()
 	{
-		$this->markTestIncomplete();
-
 		// Create a broadcast first.
-		$result = $this->api->broadcast_create(
+		$result = $this->api->create_broadcast(
 			'Test Subject',
 			'Test Content',
 			'Test Broadcast from WordPress Libraries',
 		);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		// Store Broadcast ID.
+		$broadcastID = $result['broadcast']['id'];
 
 		// Confirm the Broadcast saved.
-		$this->assertArrayHasKey('id', $result);
-		$this->assertEquals('Test Subject', $result['subject']);
-		$this->assertEquals('Test Content', $result['content']);
-		$this->assertEquals('Test Broadcast from WordPress Libraries', $result['description']);
-		$this->assertEquals(null, $result['published_at']);
-		$this->assertEquals(null, $result['send_at']);
+		$this->assertArrayHasKey('broadcast', $result);
+		$this->assertArrayHasKey('id', $result['broadcast']);
+		$this->assertEquals('Test Subject', $result['broadcast']['subject']);
+		$this->assertEquals('Test Content', $result['broadcast']['content']);
+		$this->assertEquals('Test Broadcast from WordPress Libraries', $result['broadcast']['description']);
+		$this->assertEquals(null, $result['broadcast']['published_at']);
+		$this->assertEquals(null, $result['broadcast']['send_at']);
+
+		// Update the existing broadcast.
+		$result = $this->api->update_broadcast(
+			$broadcastID,
+			'New Test Subject',
+			'New Test Content',
+			'New Test Broadcast from WordPress Libraries'
+		);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
 
-		// Delete the broadcast.
-		$this->api->broadcast_delete($result['id']);
+		// Confirm the changes saved.
+		$this->assertArrayHasKey('broadcast', $result);
+		$this->assertArrayHasKey('id', $result['broadcast']);
+		$this->assertEquals('New Test Subject', $result['broadcast']['subject']);
+		$this->assertEquals('New Test Content', $result['broadcast']['content']);
+		$this->assertEquals('New Test Broadcast from WordPress Libraries', $result['broadcast']['description']);
+		$this->assertEquals(null, $result['broadcast']['published_at']);
+		$this->assertEquals(null, $result['broadcast']['send_at']);
+
+		// Delete Broadcast.
+		$result = $this->api->delete_broadcast($broadcastID);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
 	}
 
 	/**
-	 * Test that broadcast_create() and broadcast_delete() works when valid published_at and send_at
-	 * parameters are specified.
+	 * Test that create_broadcast() works when specifying valid published_at and send_at values.
 	 *
-	 * We do all tests in a single function, so we don't end up with unnecessary Broadcasts remaining
-	 * on the ConvertKit account when running tests, which might impact
-	 * other tests that expect (or do not expect) specific Broadcasts.
+	 * @since   2.0.0
 	 *
-	 * @since   1.3.9
+	 * @return void
 	 */
-	public function testCreateAndDeletePublicBroadcastWithValidDates()
+	public function testCreatePublicBroadcastWithValidDates()
 	{
-		$this->markTestIncomplete();
-
 		// Create DateTime object.
-		$publishedAt = new \DateTime('now');
+		$publishedAt = new DateTime('now');
 		$publishedAt->modify('+7 days');
-		$sendAt = new \DateTime('now');
+		$sendAt = new DateTime('now');
 		$sendAt->modify('+14 days');
 
-		// Create a broadcast first.
-		$result = $this->api->broadcast_create(
+		// Create broadcast first.
+		$result = $this->api->create_broadcast(
 			'Test Subject',
 			'Test Content',
 			'Test Broadcast from WordPress Libraries',
@@ -1336,55 +1637,123 @@ public function testCreateAndDeletePublicBroadcastWithValidDates()
 			$publishedAt,
 			$sendAt
 		);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		// Store Broadcast ID.
+		$broadcastID = $result['broadcast']['id'];
+
+		// Set broadcast_id to ensure broadcast is deleted after test.
+		$this->broadcast_ids[] = $broadcastID;
 
 		// Confirm the Broadcast saved.
-		$this->assertArrayHasKey('id', $result);
-		$this->assertEquals('Test Subject', $result['subject']);
-		$this->assertEquals('Test Content', $result['content']);
-		$this->assertEquals('Test Broadcast from WordPress Libraries', $result['description']);
+		$this->assertArrayHasKey('id', $result['broadcast']);
+		$this->assertEquals('Test Subject', $result['broadcast']['subject']);
+		$this->assertEquals('Test Content', $result['broadcast']['content']);
+		$this->assertEquals('Test Broadcast from WordPress Libraries', $result['broadcast']['description']);
 		$this->assertEquals(
-			$publishedAt->format('Y-m-d') . 'T' . $publishedAt->format('H:i:s') . '.000Z',
-			$result['published_at']
+			$publishedAt->format('Y-m-d') . 'T' . $publishedAt->format('H:i:s') . 'Z',
+			$result['broadcast']['published_at']
 		);
 		$this->assertEquals(
-			$sendAt->format('Y-m-d') . 'T' . $sendAt->format('H:i:s') . '.000Z',
-			$result['send_at']
+			$sendAt->format('Y-m-d') . 'T' . $sendAt->format('H:i:s') . 'Z',
+			$result['broadcast']['send_at']
 		);
+	}
 
-		// Delete the broadcast.
-		$this->api->broadcast_delete($result['id']);
+	/**
+	 * Test that get_broadcast() returns the expected data.
+	 *
+	 * @since   1.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetBroadcast()
+	{
+		$result = $this->api->get_broadcast($_ENV['CONVERTKIT_API_BROADCAST_ID']);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+		$this->assertArrayHasKey('id', $result['broadcast']);
+		$this->assertEquals($result['broadcast']['id'], $_ENV['CONVERTKIT_API_BROADCAST_ID']);
 	}
 
 	/**
-	 * Test that the `broadcast_delete()` function returns a WP_Error
-	 * when no $broadcast_id parameter is provided.
+	 * Test that get_broadcast() throws a ClientException when an invalid
+	 * broadcast ID is specified.
 	 *
-	 * @since   1.3.9
+	 * @since   2.0.0
+	 *
+	 * @return void
 	 */
-	public function testDeleteBroadcastWithNoBroadcastID()
+	public function testGetBroadcastWithInvalidBroadcastID()
 	{
-		$this->markTestIncomplete();
+		$result = $this->api->get_broadcast(12345);
+		$this->assertInstanceOf(WP_Error::class, $result);
+	}
+
+	/**
+	 * Test that get_broadcast_stats() returns the expected data.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetBroadcastStats()
+	{
+		$result = $this->api->get_broadcast_stats($_ENV['CONVERTKIT_API_BROADCAST_ID']);
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertIsArray($result);
+
+		$this->assertArrayHasKey('broadcast', $result);
+		$this->assertArrayHasKey('id', $result['broadcast']);
+		$this->assertArrayHasKey('stats', $result['broadcast']);
+		$this->assertEquals($result['broadcast']['stats']['recipients'], 1);
+		$this->assertEquals($result['broadcast']['stats']['open_rate'], 0);
+		$this->assertEquals($result['broadcast']['stats']['click_rate'], 0);
+		$this->assertEquals($result['broadcast']['stats']['unsubscribes'], 0);
+		$this->assertEquals($result['broadcast']['stats']['total_clicks'], 0);
+	}
 
-		$result = $this->api->broadcast_delete('');
+	/**
+	 * Test that get_broadcast_stats() throws a ClientException when an invalid
+	 * broadcast ID is specified.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @return void
+	 */
+	public function testGetBroadcastStatsWithInvalidBroadcastID()
+	{
+		$result = $this->api->get_broadcast_stats(12345);
 		$this->assertInstanceOf(WP_Error::class, $result);
-		$this->assertEquals($result->get_error_code(), $this->errorCode);
-		$this->assertEquals('broadcast_delete(): the broadcast_id parameter is empty.', $result->get_error_message());
 	}
 
 	/**
-	 * Test that the `broadcast_delete()` function returns a WP_Error
-	 * when an invalid $broadcast_id parameter is provided.
+	 * Test that update_broadcast() throws a ClientException when an invalid
+	 * broadcast ID is specified.
 	 *
-	 * @since   1.3.9
+	 * @since   1.0.0
+	 *
+	 * @return void
 	 */
-	public function testDeleteBroadcastWithInvalidBroadcastID()
+	public function testUpdateBroadcastWithInvalidBroadcastID()
 	{
-		$this->markTestIncomplete();
+		$result = $this->api->update_broadcast(12345);
+		$this->assertInstanceOf(WP_Error::class, $result);
+	}
 
-		$result = $this->api->broadcast_delete(12345);
+	/**
+	 * Test that delete_broadcast() throws a ClientException when an invalid
+	 * broadcast ID is specified.
+	 *
+	 * @since   1.0.0
+	 *
+	 * @return void
+	 */
+	public function testDeleteBroadcastWithInvalidBroadcastID()
+	{
+		$result = $this->api->delete_broadcast(12345);
 		$this->assertInstanceOf(WP_Error::class, $result);
-		$this->assertEquals($result->get_error_code(), $this->errorCode);
-		$this->assertEquals('Not Found: The entity you were trying to find doesn\'t exist', $result->get_error_message());
 	}
 
 	/**
@@ -2252,4 +2621,38 @@ function( $response ) use ( $httpCode, $httpMessage, $body ) { // phpcs:ignore G
 			}
 		);
 	}
+
+	/**
+	 * Helper method to assert the given key exists as an array
+	 * in the API response.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @param   array  $result     API Result.
+	 * @param   string $key        Key.
+	 */
+	private function assertDataExists($result, $key)
+	{
+		$this->assertNotInstanceOf(WP_Error::class, $result);
+		$this->assertArrayHasKey($key, $result);
+		$this->assertIsArray($result[ $key ]);
+	}
+
+	/**
+	 * Helper method to assert pagination object exists in response.
+	 *
+	 * @since   2.0.0
+	 *
+	 * @param   array $result     API Result.
+	 */
+	private function assertPaginationExists($result)
+	{
+		$this->assertArrayHasKey('pagination', $result);
+		$pagination = $result['pagination'];
+		$this->assertArrayHasKey('has_previous_page', $pagination);
+		$this->assertArrayHasKey('has_next_page', $pagination);
+		$this->assertArrayHasKey('start_cursor', $pagination);
+		$this->assertArrayHasKey('end_cursor', $pagination);
+		$this->assertArrayHasKey('per_page', $pagination);
+	}
 }
diff --git a/tests/wpunit/ResourceTest.php b/tests/wpunit/ResourceTest.php
index 10e2890..be50a47 100644
--- a/tests/wpunit/ResourceTest.php
+++ b/tests/wpunit/ResourceTest.php
@@ -32,27 +32,12 @@ public function setUp(): void
 		parent::setUp();
 
 		// Include class from /src to test.
+		require_once 'src/class-convertkit-api-traits.php';
+		require_once 'src/class-convertkit-api.php';
 		require_once 'src/class-convertkit-resource.php';
 
 		// Initialize the classes we want to test.
 		$this->resource = new ConvertKit_Resource();
-
-		// Mock the data that the resource class would receive from the WordPress options table
-		// (and therefore the ConvertKit APIs) to perform tests on.
-		$this->resource->resources = [
-			2780977 => [
-				'id'           => 2780977,
-				'name'         => 'Z Name', // 'name' used by forms, landing pages, products, tags.
-				'title'        => 'Z Name', // 'title' used by posts.
-				'published_at' => '2022-01-24T00:00:00.000Z', // used by posts.
-			],
-			2765139 => [
-				'id'           => 2765139,
-				'name'         => 'A Name', // 'name' used by forms, landing pages, products, tags.
-				'title'        => 'A Name', // 'title' used by posts.
-				'published_at' => '2022-05-03T14:51:50.000Z', // used by posts.
-			],
-		];
 	}
 
 	/**
@@ -76,6 +61,9 @@ public function tearDown(): void
 	 */
 	public function testGet()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Call resource class' get() function.
 		$result = $this->resource->get();
 
@@ -99,6 +87,9 @@ public function testGet()
 	 */
 	public function testGetWithValidOrderBy()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Define order_by = title.
 		$this->resource->order_by = 'title';
 
@@ -125,6 +116,9 @@ public function testGetWithValidOrderBy()
 	 */
 	public function testGetWithInvalidOrderBy()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Define order_by with an invalid value (i.e. an array key that does not exist).
 		$this->resource->order_by = 'invalid_key';
 
@@ -151,6 +145,9 @@ public function testGetWithInvalidOrderBy()
 	 */
 	public function testGetWithValidOrder()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Define order to be descending.
 		$this->resource->order_by = 'name';
 		$this->resource->order    = 'desc';
@@ -178,6 +175,9 @@ public function testGetWithValidOrder()
 	 */
 	public function testGetWithValidOrderByAndOrder()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Define order to be descending.
 		$this->resource->order_by = 'published_at';
 		$this->resource->order    = 'desc';
@@ -205,6 +205,9 @@ public function testGetWithValidOrderByAndOrder()
 	 */
 	public function testGetBy()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Call resource class' get_by() function.
 		$result = $this->resource->get_by('name', 'Z Name');
 
@@ -229,6 +232,9 @@ public function testGetBy()
 	 */
 	public function testGetByMultipleValues()
 	{
+		// Mock data from get().
+		$this->mockData();
+
 		// Call resource class' get_by() function.
 		$result = $this->resource->get_by('name', [ 'A Name', 'Z Name' ]);
 
@@ -246,4 +252,96 @@ public function testGetByMultipleValues()
 		$this->assertEquals('A Name', reset($result)[ $this->resource->order_by ]);
 		$this->assertEquals('Z Name', end($result)[ $this->resource->order_by ]);
 	}
+
+	/**
+	 * Tests that the refresh() function returns resources in an array, and that they are
+	 * in alphabetical ascending order by default.
+	 *
+	 * @since   2.0.0
+	 */
+	public function testRefresh()
+	{
+		// Assign resource type and API.
+		$this->resource->settings_name = 'convertkit_resource_forms';
+		$this->resource->type          = 'forms';
+		$this->resource->api           = new ConvertKit_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Call resource class' refresh() function.
+		$result = $this->resource->refresh();
+
+		// Assert result is an array.
+		$this->assertIsArray($result);
+
+		// Assert array keys are preserved.
+		$this->assertArrayHasKey($_ENV['CONVERTKIT_API_FORM_ID'], $result);
+
+		// Assert order of data is in ascending alphabetical order.
+		$this->assertEquals('AAA Test', reset($result)[ $this->resource->order_by ]);
+		$this->assertEquals('WooCommerce Product Form', end($result)[ $this->resource->order_by ]);
+
+		// Confirm resources stored in WordPress options.
+		$resources = get_option($this->resource->settings_name);
+
+		// Assert result is an array.
+		$this->assertIsArray($resources);
+
+		// Assert array keys are preserved.
+		$this->assertArrayHasKey($_ENV['CONVERTKIT_API_FORM_ID'], $resources);
+	}
+
+	/**
+	 * Tests that the refresh() function returns resources in an array, and that they are
+	 * in alphabetical ascending order by default.
+	 *
+	 * @since   2.0.0
+	 */
+	public function testRefreshWithInvalidType()
+	{
+		// Assign resource type and API.
+		$this->resource->type = 'not-a-valid-resource-type';
+		$this->resource->api  = new ConvertKit_API(
+			$_ENV['CONVERTKIT_OAUTH_CLIENT_ID'],
+			$_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'],
+			$_ENV['CONVERTKIT_OAUTH_ACCESS_TOKEN'],
+			$_ENV['CONVERTKIT_OAUTH_REFRESH_TOKEN']
+		);
+
+		// Call resource class' refresh() function.
+		$result = $this->resource->refresh();
+
+		// Assert result is a WP_Error.
+		$this->assertInstanceOf(WP_Error::class, $result);
+		$this->assertEquals($result->get_error_code(), 'convertkit_resource_refresh_error');
+		$this->assertEquals($result->get_error_message(), 'Resource type ' . $this->resource->type . ' is not supported in ConvertKit_Resource class.');
+	}
+
+	/**
+	 * Defines an array of resources when mocking get() requests in tests.
+	 *
+	 * @since   2.0.0
+	 */
+	private function mockData()
+	{
+		// Mock the data that the resource class would receive from the WordPress options table
+		// (and therefore the ConvertKit APIs) to perform tests on.
+		$this->resource->resources = [
+			2780977 => [
+				'id'           => 2780977,
+				'name'         => 'Z Name', // 'name' used by forms, landing pages, products, tags.
+				'title'        => 'Z Name', // 'title' used by posts.
+				'published_at' => '2022-01-24T00:00:00.000Z', // used by posts.
+			],
+			2765139 => [
+				'id'           => 2765139,
+				'name'         => 'A Name', // 'name' used by forms, landing pages, products, tags.
+				'title'        => 'A Name', // 'title' used by posts.
+				'published_at' => '2022-05-03T14:51:50.000Z', // used by posts.
+			],
+		];
+	}
 }