Error code 500121

Question

Cannot login on my Authenticator app which prevents me from logging in on my work computer. When I try to log in it gives me an Authenticator app code which I can’t use because I’m not logged in. What should I do?

Answer 1

Hello @Mark Bumstead

Thank you for reaching out to the Microsoft Q&A forum. 

To better understand your issue, could you please help clarify a few details:

1. Are you an end user or an administrator in your organization?
2. Are you trying to sign in to your work account on a new device or after changing your phone?
3. Do you have any alternative authentication methods available (such as SMS, phone call, or backup codes)?
4. Are you able to access the Microsoft Authenticator app at all, or are you completely locked out?

This will help me to determine whether the issue is related to Multi-Factor Authentication configuration or access to your authentication methods. In many cases, this type of issue is related to Multi-Factor Authentication (MFA) access, but I'd like to confirm your scenario first before suggesting the next steps.

Looking forward to your response.

Answer 2

Error 500121 indicates that authentication did not complete, typically because the Microsoft Authenticator app cannot finish the sign-in.

Follow these steps:

1. Open Microsoft Authenticator on the phone and make sure the app is unlocked. If the app is locked, the prompt or code entry box may not appear.
2. Check that notifications are enabled for Microsoft Authenticator on the device. If notifications are silent or disabled, the approval prompt may be missed. Also check SMS messages in case a code was sent there.
3. Confirm the phone has a working internet connection. If needed, switch between Wi‑Fi and mobile data and try again.
4. Make sure the device date and time are set correctly and that the latest version of Microsoft Authenticator is installed from the app store.
5. If the sign-in is still blocked after multiple attempts, wait a while before trying again or use a different MFA method (such as SMS or another registered method) if one is available.
6. If no alternative MFA method works or is available, contact the organization’s IT administrator or Help desk and ask them to reset or clear the MFA/authentication methods for the account in Microsoft Entra ID. After they reset MFA, the next sign-in will prompt to re-register the Authenticator app.
7. If the account is a business/education account and the user is the only administrator and cannot sign in at all, call Microsoft Support using the regional customer service phone number and request the Data Protection team to help regain access and reset MFA for the tenant admin account.

If the password itself is forgotten, use the organization’s password reset process or the provided password reset link, then repeat the steps above.

---

References:

• Authentication did not complete
• Troubleshoot problems with Microsoft Authenticator
• Common problems with two-step verification for a work or school account
• I cant log in to my business account because it is requiring Authenticator app which I do not have - 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
• Microsoft authenticator sending me into a spiral - Microsoft Q&A
• I need to reset my mfa methods - Microsoft Q&A
• Requesting a Tenant Admin MFA Reset - Microsoft Q&A
• Authenticator Did Not Complete Login