diff --git a/Api/Data/ResultInterface.php b/Api/Data/ResultInterface.php
index cb076ed..f991823 100644
--- a/Api/Data/ResultInterface.php
+++ b/Api/Data/ResultInterface.php
@@ -1,18 +1,53 @@
 <?php
 
+declare(strict_types=1);
+
 namespace MageOS\AsyncEvents\Api\Data;
 
 interface ResultInterface
 {
+    /**
+     * Getter for is_successful
+     *
+     * @return bool
+     */
     public function getIsSuccessful(): bool;
 
+    /**
+     * Setter for is_successful
+     *
+     * @param bool $isSuccessful
+     * @return void
+     */
     public function setIsSuccessful(bool $isSuccessful): void;
 
+    /**
+     * Getter for is_retryable
+     *
+     * @return bool
+     */
     public function getIsRetryable(): bool;
 
+    /**
+     * Setter for is_retryable
+     *
+     * @param bool $isRetryable
+     * @return void
+     */
     public function setIsRetryable(bool $isRetryable): void;
 
+    /**
+     *  Getter for retry_after
+     *
+     * @return int|null
+     */
     public function getRetryAfter(): ?int;
 
+    /**
+     * Setter for retry_after
+     *
+     * @param int $retryAfter
+     * @return void
+     */
     public function setRetryAfter(int $retryAfter): void;
 }
diff --git a/Service/AsyncEvent/HttpNotifier.php b/Service/AsyncEvent/HttpNotifier.php
index e79d5bb..30521de 100644
--- a/Service/AsyncEvent/HttpNotifier.php
+++ b/Service/AsyncEvent/HttpNotifier.php
@@ -82,12 +82,12 @@ public function notify(AsyncEventInterface $asyncEvent, array $data): NotifierRe
                 $notifierResult->setResponseData($exceptionMessage);
                 $notifierResult->setIsRetryable(true);
 
-                // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After
                 if ($response->hasHeader('Retry-After')) {
                     $retryAfter = $response->getHeader('Retry-After')[0];
-                    $notifierResult->setRetryAfter((int) $retryAfter);
+                    if (is_numeric($retryAfter)) {
+                        $notifierResult->setRetryAfter((int) $retryAfter);
+                    }
                 }
-
             } else {
                 $notifierResult->setResponseData(
                     $exception->getMessage()