How to fix error code 500121

Dear @Yates, Sierra,

Welcome to Microsoft Q&A. 

Thank you for your question. Based on the error code 500121 you mentioned, this issue is related to Multi‑Factor Authentication (MFA). This error indicates that the strong authentication request could not be completed, for example because the MFA prompt was not approved, timed out, or the Authenticator configuration is no longer valid.

If you are not an administrator, please contact your school or organization’s IT administrator and ask them to reset or re‑register your MFA methods in Microsoft Entra ID

Please have your administrator follow the steps shown in the following article: Manage authentication methods for Microsoft Entra multi-factor authentication - Microsoft Entra ID …

Please note that forum moderators have no control over user accounts, especially when it comes to logging in to your account, resetting your password, changing your access, etc.

Therefore, if you are the only administrator in your organization, then you need to involve Microsoft data protection team. Please try to find the related hotline number to call the frontline let them raise a ticket for you: Customer service phone numbers - Microsoft Support

In some countries, this is an automated conversation: First, when you call the hotline, they will ask you what kind of problem you are struggling with.

Answer: Authenticator.

A: What products do you use?

B: Office 365 for business.

Verification: Education or company account?

B: For companies

A: Are you an administrator?

B: Yes.

A: Are there any other administrators in your organization?

B: No.

A: I need one.... Service request?

B: Yes

If your organization's Office 365 Business/Education subscription is from a partner or reseller, and the global administrator is unable to open a service request on your end, contact the reseller's support provider to help open a service request on behalf of you instead.

If you still cannot reach to agent, there is still a workaround, you might consider registering for a new tenant by signing up for a trial subscription via this link Compare All Microsoft 365 Plans | Microsoft. This would allow you to create a new tenant following the provided prompts. Once set up, you can access the admin console of the new tenant and submit a support ticket requesting to speak with the Data Protection team on behalf of your previous tenant.

Please remember to cancel the trial subscription once your issue is resolved to avoid any unintended charges.

I understand that this entire process can feel long and complicated, and I truly appreciate your patience while working through it. These steps are in place to protect the security of your account, so I hope you can understand why they are required. I sincerely hope you’ll be able to regain access to your account soon. If you need help at any point, or if you have any questions during the process, please feel free to reach out, I’m always here and happy to assist.

Thank you again for your understanding and patience.

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To resolve error code 500121 with the Microsoft Authenticator app, you can try the following steps:

1. Check App Permissions: Ensure that the Authenticator app has the necessary permissions to function correctly on your device.
2. Update the App: Make sure that the Microsoft Authenticator app is updated to the latest version available on your device's app store.
3. Reinstall the App: If the app is still not providing a verification code, consider uninstalling and then reinstalling the Microsoft Authenticator app.
4. Verify Account Settings: Ensure that your account is correctly set up in the app. If you have recently changed your phone or account settings, you may need to reconfigure the app.
5. Contact Support: If none of the above steps work, you may need to contact Microsoft support for further assistance, especially if you are locked out of your account.

These steps should help you troubleshoot and potentially resolve the issue with the verification code not being displayed in the Authenticator app.

References:

• Microsoft Authenticator app doesn't show 6-digit OTP code - Microsoft Q&A
• I have a Micrsoft business account and I am the admin and the only user registered under this account. I can't log in because i have replaced my phone and the authenticator doesn't work. - Microsoft Q&A