This article explains why the following error occurs in system logs when a user attempts to authenticate using Short Message Service (SMS) for Multi-Factor Authentication (MFA) while using Twilio as messaging service:

The 'To' phone number: <phone number>, is not currently reachable using the 'From' phone number: <phone number> via SMS.

Sample tenant log:

"provider_error": {
"errorCode": 21612,
"message": "The 'To' phone number: +**********, is not currently reachable using the 'From' phone number: +************ via SMS."
}

• Multi-Factor Authentication (MFA)

• SMS
• Twilio
• Error 21612

This error is sent from Twilio in response to an SMS delivery attempt. The message indicates that the destination phone number cannot be reached. Common reasons for this include issues with Sender ID restrictions or phone number formatting.

The error originates from Twilio's service, not the application. To resolve the issue, consult the troubleshooting steps provided in Twilio's official documentation for Error 21612. If the provided steps do not resolve the issue, contact Twilio support for further assistance.