The "Messaging Error – SMS" trigger lets you start workflows in response to failed SMS delivery attempts. When an SMS cannot be delivered, the system generates a specific error code indicating the reason for failure, whether that's an invalid number, a carrier issue, or blocked content. Read on to find out more about this trigger and how to add it to your workflow.

Implementing the Messaging Error Trigger

To add this trigger to your workflows, go to the Automation > Workflows tab. From there, either choose an existing workflow or create a new one.

Next, click the "Add New Trigger" button and search for and select "Messaging Error - SMS" as the trigger event.

Give the trigger a clear, descriptive name so it's easy to identify within your workflow.

Add filters to narrow the trigger down to specific error codes. This lets you respond only to the messaging failures that matter to you, so the workflow only fires under the right conditions.

The following error codes are supported. You can include or exclude any of them depending on your needs:

  • 21211: The "To" number is invalid or improperly formatted.
  • 21408: Messaging not permitted to the specified region.
  • 21606: The "From" number is invalid or improperly formatted.
  • 21610: The recipient has opted out by replying STOP.
  • 21614: The "To" number is not a valid mobile number.
  • 21635: The "To" number is a landline and cannot receive SMS.
  • 21661: The "From" number is not capable of sending SMS.
  • 30002: The sub-account has been suspended and cannot send messages.
  • 30003: Unreachable/Out of Service Number
  • 30004: Do not want SMS/DND enabled
  • 30005: User Inactive/Number does not exist
  • 30006: Landline/Incapable of receiving SMS
  • 30007: Carrier Violation
  • 30008: An unknown error occurred during message delivery.
  • 30011: MMS is not supported by the recipient's device or region.
  • 30023: Daily A2P messaging limit reached in the U.S.
  • 30032: Toll-Free Number not verified
  • 30033: The A2P campaign has been suspended or deleted.
  • 30034: A2P Registration Pending on Number
  • 30037: Outbound messaging has been disabled for this account.

Once you're happy with the setup, save the trigger to your workflow.

This gives you better message deliverability and contact quality, cuts down on wasted sends to unreachable or non-compliant numbers, gives you more control over how your system handles delivery failures, and reduces the need to contact support for error resolution.

Using this trigger, you can automatically respond to undelivered messages with tailored workflows, such as notifying internal teams, retrying the message, or escalating the issue for further review. This improves communication reliability and helps you proactively manage messaging errors, keeping the experience smooth for your customers.