Users trying add phone to MFA failing

Question

I have allowed phone as an MFA method but when a user tries to add a phone they get a vague error not allowing the phone to be added. Tried in school and out of the building. Even global admins can't add phone as MFA option. Tried searching the Correlation ID's and no luck. All other allowed options for MFA work fine.

Answer 1

Because other MFA methods work and the issue occurs for all users (including global admins), the problem is most likely with how phone-based methods are configured or with the phone numbers themselves, not with MFA in general.

Use the following checks and remediation steps:

1. Confirm phone is actually allowed as a method
   • In Microsoft Entra admin center, verify that the MFA/Authentication Methods policy really has Phone (call/SMS) enabled for the affected users/groups.
   • If using the new Authentication Methods policies, ensure there is no conditional scoping that excludes these users.
2. Verify numbers are being added in a valid format
   • When admins add a phone for a user in Entra admin center, they must:
     • Go to Entra ID → Users → <user> → Authentication methods → + Add authentication method.
     • Select Phone number.
     • Enter the number in valid E.164 format, for example +1 4255551234.
   • Phone extensions and VOIP numbers are not supported for MFA. If users are trying to add numbers like +1 4255551234X12345 or VOIP, the platform will strip extensions or fail.
3. Check that the tenant is not blocking phone-based MFA
   • If users are not receiving SMS/calls when testing, follow the guidance for “We didn't receive a response” and “Account verification system is having trouble” errors:
     • Make sure the phone works and has service.
     • Confirm correct country/region code and number in security verification settings.
     • Try Other verification options to confirm the account itself is healthy.
   • If SMS/calls never arrive for any user, there may be a provider or regional issue; in that case, open a support ticket with Microsoft.
4. Check for user-level blocks or risk-based blocks
   • For affected users, in Entra admin center:
     • Go to Entra ID → Users → <user> and verify Block sign in is not enabled.
   • If users are not getting codes at all and there is unusual sign-in activity, they may be temporarily blocked from receiving codes due to risk protection. In that case, wait for the block to clear and avoid repeated requests.
5. If the issue persists for all users including admins
   • Because correlation IDs are not documented publicly, the next step is to open a support case with Microsoft. Similar issues (for example, SMS “bad reputation” or global SMS problems) have required Microsoft support intervention to clear blocks or adjust backend configuration.

Once phone numbers are added successfully, users can also manage their own methods at My Sign-Ins | Security info (https://mysignins.microsoft.com/security-info) and change phone numbers there.

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References:

• Manage user authentication methods for Microsoft Entra multifactor authentication
• Set up a phone call as your verification method
• "We didn't receive a response" error message when you try to sign in by using Azure Multi-Factor Authentication
• "Account verification system is having trouble" error message when you try to sign in by using a work or school account
• You don't receive a text or voice call that contains the verification code for Microsoft Entra multifactor authentication
• Common problems with two-step verification for a work or school account