Troubleshooting Missing AWS SNS Subscription in n8n Workflow

Below is some guidance on troubleshooting your issue:

What’s Happening

The error message:

The resource you are requesting could not be found ( Sender `NotFound` Subscription does not exist 667f4962-bd1f-5d49-a144-16d810353c91 )

indicates that the AWS SNS subscription n8n is trying to use can’t be found. In other words, the subscription associated with your workflow is either missing or no longer valid.

Possible Causes

• Subscription Removed or Expired:
  The subscription might have been manually removed or expired on the AWS side. Even if another workflow using a different SNS topic works, it’s possible that only one of the subscriptions became invalid.

• Webhook Resubscription Issue:
  Toggling the workflow off and on can trigger re-subscription. If the topic or subscription configuration isn’t set correctly during this reactivation, SNS might return a “NotFound” error after processing a couple of events.

• Misconfigured SNS Settings:
  Although your IAM settings are the same, there might be differences in how the SNS topics or endpoints are configured, such as issues with the ARN or webhook URL.

Recommended Steps

1. Verify the Subscription in AWS:

   • Log in to the AWS SNS console.
   • Check that the subscription ARN for the problematic SNS topic exists and is in a confirmed status.
   • If the subscription is missing, you may need to recreate it manually or allow n8n to register it again.

2. Review Workflow Configuration in n8n:

   • Confirm that the webhook URL and any topic-specific settings match what is expected on AWS.
   • Check if reactivating the workflow triggers n8n to resubscribe and, if so, ensure that the registration process completes without errors.

3. Examine Logs and Credentials:

   • Look into the n8n logs for any additional error messages that might provide more details.
   • Verify that the credentials and IAM policies used by both workflows are correct and include permission to manage subscriptions.

4. Resubscribe or Reset the Connection:

   • As a workaround, toggle the workflow off, double-check the SNS subscription settings in AWS, and then re-enable the workflow to force a re-registration.
   • If issues persist, consider deleting the existing (problematic) subscription from AWS and allowing n8n to create a new one.

Conclusion

This error typically means the AWS SNS subscription which your workflow relies on does not exist. By verifying and correcting the subscription in AWS and ensuring your workflow’s configuration properly matches, you should be able to resolve the issue. If the problem continues, additional details from the n8n logs can help pinpoint the underlying cause.