Microsoft 365 and Office | Install, redeem, activate | For business | Other
Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
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Dear Lotfi
Good day, and I appreciate the detailed description of your issue. As a forum moderator, I genuinely wish I could directly access your account or step into the backend systems and resolve this for you. Unfortunately, my role here is limited to providing general guidance and solutions that you can apply from your side.
From my research, Error 399287 means that Azure has blocked your phone number for SMS verification due to a"bad reputation" flag. When this happens, SMS or call-based MFA verification cannot be completed, which prevents you from signing in to your account. To recover access, you will need your IT administrator (or Microsoft Support) to reset your MFA and unblock the phone number from the Microsoft Entra Admin Center. If you don't know who your IT administrator is, please refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support
For detailed instructions, please refer to this Microsoft guide: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID
Once the block is lifted, please go to My Sign-Ins | Security Info and add Microsoft Authenticator as your sign-in method. Using Authenticator for future logins is more reliable than SMS and can help avoid similar reputation-based blocks going forward.
If your IT administrator is unable to resolve this from their side, please ask them to submit a support ticket to the Microsoft Data Protection team on your behalf. For detailed instructions on how to get support, please refer to Get support - Microsoft 365 admin.
When opening the ticket, please share all the information you have provided here (including Error 399287, the account affected, and the phone number involved) so that the support case can be routed to the appropriate team as quickly as possible.
I know this isn't the answer you were hoping for, and it's disappointing when the solutions aren't straightforward. Please know that as a forum moderator, directing you to the correct, specialized support is the most effective help I can provide from my position. I truly hope you get your issue resolved swiftly. Wishing you all the best.
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