Reapply "Revert swagger"

This reverts commit 416d826.

specifications/api/swagger.yaml

@@ -5112,6 +5112,20 @@ x-errTxNotInNodeEra: &errTxNotInNodeEra
       type: string
       enum: ["tx_not_in_node_era"]
 
+x-errBalanceTxConflictingNetworks: &errBalanceTxConflictingNetworks
+  <<: *responsesErr
+  title: balance_tx_conflicting_networks
+  properties:
+    message:
+      type: string
+      description: |
+        There are withdrawals for multiple networks
+        (e.g. both mainnet and testnet) in the provided transaction.
+        This makes no sense, and I'm confused.
+    code:
+      type: string
+      enum: ["balance_tx_conflicting_networks"]
+
 x-errTranslationByronTxOutInContext: &errTranslationByronTxOutInContext
   <<: *responsesErr
   title: translation_byron_tx_out_in_context
@@ -6780,6 +6794,7 @@ x-responsesBalanceTransaction: &responsesBalanceTransaction
           oneOf:
             - <<: *errAlreadyWithdrawing
             - <<: *errNodeNotYetInRecentEra
+            - <<: *errBalanceTxConflictingNetworks
             - <<: *errBalanceTxExistingCollateral
             - <<: *errBalanceTxExistingKeyWitnesses
             - <<: *errBalanceTxExistingReturnCollateral