Microsoft 365 Developer Program Go to your E5 Sandbox Verify Entity Error

Question

Hi,

I have Microsoft 365 Developer Program, when I click "Go to your E5 Sandbox", I can login with my admin account, but it show the verify phone number, I click on my phone number, and it failed:

Error Code: 399287

Request Id: [Moderator note: personal info removed]

Correlation Id: [Moderator note: personal info removed]

Timestamp: 2026-03-30T06:58:20Z

Anyone can help me?

Thanks

Answer 1

Please note that the Microsoft Q&A forum is a public platform. To protect personal data, moderators may edit questions to remove or hide any personal or organizational information included in the description. Kindly ensure that you redact sensitive details when posting error messages or other information in the future. You will find your personal information in private messages instead.

Dear Nguyen Chi Thanh

First, I recommend reviewing the AI‑generated response on your post, as it aligns closely with my own understanding of the issue.

You may also find the following related thread helpful: https://learn.microsoft.com/en-us/answers/questions/5823773/urgent-locked-out-of-microsoft-365-developer-tenan

In that thread, Microsoft staff outline two effective ways to contact the Data Protection team for further assistance.

Please note that this process may take longer than usual (approximately 7–14 working days), as the Data Protection team is currently handling a high volume of requests. As this is a community forum, and as a forum moderator, I do not have access to Microsoft internal systems and am unable to expedite this process.

I hope this information is helpful.

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Answer 2

Error code 399287 when verifying by SMS indicates that Azure has blocked the phone number for SMS verification because it has been flagged with a “bad reputation.” In this state, SMS-based MFA for that number will consistently fail.

The resolution in similar cases has required intervention from Microsoft support to reset MFA and clear the reputation flag on the phone number. Self-service changes (retrying, password reset, or alternate sign-in attempts using the same blocked number) do not resolve it.

Action steps:

1. Collect the details already shown (error code 399287, Request Id, Correlation Id, Timestamp, tenant information, and the affected phone number).
2. Open a support case with Microsoft (for a Microsoft 365 Developer Program tenant, use the standard Microsoft 365 support channel from the admin center) and clearly state that SMS verification fails with error 399287 and that the number appears to be blocked due to “bad reputation.”
3. Ask support to have the Microsoft data protection/identity team reset MFA for the account and remove the bad reputation flag from the phone number.
4. After support confirms the reset, attempt sign-in again and complete MFA using SMS or, preferably, add an alternative MFA method (such as the Microsoft Authenticator app) once access is restored.

Until support clears the flag, the SMS verification for that number will continue to fail, so direct support involvement is required.

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References:

• Microsoft 365 Developer Program FAQ
• "We did not receive the expected response" error message when you try to sign in by using Azure Multi-Factor Authentication
• 399287 - Microsoft Q&A Unable to Verify Identity for Azure Login – Error 399287
• Azure has blocked myphone number for SMS verification due to a “bad reputation” flag - Microsoft Q&A