SMS Notification Error: [631] Mobile network operator error

Issue

SMS message fails to deliver and logs indicate the following error

Notification Error; [631] Mobile network operator error

Environment 

• All versions of xMatters
• SMS Notifications

Answer

This error indicates that a message could not be delivered due to an infrastructure error at the carrier level. The error may resolve without intervention after a short period of time. If the error persists, please Submit a Request with Customer Support for investigation.

Fix

Consider using the xMatters mobile app.  Although we continue to work with carriers, providers, and aggregators to lobby for the best end-user experience over SMS, we recommend the xMatters mobile app as a more reliable alternative.