30126: Your 10DLC number failed to be registered

This error means Twilio could not complete the backend registration or deregistration of your US A2P 10DLC phone number. Number registration starts when you add or remove a number from a Messaging Service that is associated with an approved US A2P campaign. If the number reaches FAILURE, an unexpected error occurred during configuration with ecosystem partners.

• The number registration or deregistration request reached the FAILURE status during backend configuration with ecosystem partners.
• The number was added to or removed from a Messaging Service associated with an approved campaign, which triggered a new number registration cycle that did not complete successfully. (help.twilio.com)
• Repeatedly removing, re-adding, or moving 10DLC numbers between Messaging Services or accounts can trigger additional registration and deregistration cycles and lead to delays or errors. (help.twilio.com)

• Request the A2P registration status CSV report in Console and verify whether the number is FAILURE, PENDING_REGISTRATION, PENDING_DEREGISTRATION, or UNREGISTERED. The report includes the phone number, Campaign SID, and Messaging Service SID so you can confirm the current state before taking action.
• If the number is UNREGISTERED, add it to a Messaging Service that is associated with a verified A2P campaign, then wait for number registration to finish.
• Avoid removing, re-adding, or moving the number while registration is being processed. Each change starts another provisioning cycle and can add more time or create additional errors. (help.twilio.com)
• If the number remains in FAILURE, contact Support for investigation.

• A2P 10DLC registration application quickstart
• Troubleshooting A2P phone number registration issues
• A2P 10DLC Number Registration Best Practices