Error 399287 MFA SMS verification failed

CUONG NGUYEN 0 Reputation points
2026-09-21T06:37:44.23+00:00

Hello,   I am locked out of my Microsoft 365 E5 Developer Sandbox tenant.   I know the administrator password, but SMS is the only MFA method registered for the Global Administrator account.   SMS verification fails with:   Error Code: 399287   I am the only Global Administrator and I cannot access the tenant to reset or register another authentication method.   Please create a support case for the affected tenant and escalate the MFA lockout issue to the Data Protection team.   I can provide the tenant information, affected administrator account, Request ID, Correlation ID, and Timestamp privately.   Thank you.

Microsoft 365 and Office | Subscription, account, billing | For business | Other
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  1. Jayden-P 3,045 Reputation points Independent Advisor
    2026-09-21T06:42:56.1966667+00:00

    Please note that this forum is not Microsoft support, this is a user-to-user support forum. Therefore, I cannot directly escalate this for you. However, I can guide you how to contact Data Protection team.

    Hi @CUONG NGUYEN

    In this situation, you will need to contact Data Protection team. They can help you regain access to your tenant.

    Please visit the following page and reach out to phone number via: Customer service phone numbers - Microsoft Support

    From what I know, you will need to get past the initial AI system to reach the live support team. You can refer to the guide below for tips on how to get through more easily:User's image

    If you have tried phone support and it's not working, please follow this link to create a trial tenant: https://www.microsoft.com/microsoft-365/business/microsoft-365-business-basic?msockid=3eb6980b5c6860e63a588d0c5d1761d6 - after that you will be able to access to Microsoft 365 Admin Center to raise the ticket

    Assuming that you have already created an account after registering a free trial and you can go to Microsoft 365 admin center and click "Help & support" icon to raise your ticket.      

    User's image

    Please mention that you are raising ticket on behalf of the affected tenant that you do not have access to.

    On the other hand, if you do create the trial and it resolves the issue, please remember to cancel the subscription afterward to avoid any related charges. 

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