MFA & Verification Issues

How to Fix Microsoft Authenticator Error 500121 When Switching Directories

Maira Mehtab Oct 13, 2026 868 views

Question details

The user needs to resolve an authentication failure (Error 500121) that happens when switching directories in Microsoft Entra with a multi-tenant account.

How to Fix Microsoft Authenticator Error 500121 When Switching Directories

Product: Microsoft Authenticator
Device & OS: not provided
Scenario: Switching Microsoft Entra directories for an account that belongs to multiple tenants.
Observed behavior: The authentication fails with Error 500121 and displays an incorrect verification code.

Before you start

Ensure you have access to a secondary sign-in method or know the contact information for your organization's Global Administrator to reset your multi-factor authentication settings.

Solution 1Recommended

Remove and Re-register the Affected Account in Microsoft Authenticator

Use this method to clear out the broken configuration and register your account freshly with the correct directory.

This is the most common fix for users experiencing tenant mismatches in the Authenticator app.

Open Microsoft Authenticator

Launch the Microsoft Authenticator app on your mobile device.

Remove the account

Select the work or school account experiencing Error 500121, tap the settings (gear) icon in the top right, and choose 'Remove account'.

Sign out of your session

On your computer or application, completely sign out of the affected Microsoft account.

Sign back in and re-register

Sign in again using your username and password. Follow the on-screen prompts to set up Microsoft Authenticator anew for the correct directory.

Remove and Re-register the Affected Account in Microsoft Authenticator

Tip: If another verification method is available, click 'Other ways to sign in' during the login process to bypass the broken Authenticator prompt temporarily.

Solution 2

Request an MFA Reset from a Global Administrator

If you are locked out completely, an IT administrator must reset your authentication methods from the backend.

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Frequently Asked Questions

Why am I getting Error 500121 when switching directories?

This error typically occurs when there is a mismatch or token conflict in Microsoft Authenticator for an account that belongs to multiple Microsoft Entra tenants. The app generates a verification code for the wrong directory, causing the sign-in to fail.

Can I fix Error 500121 if I am the only global administrator?

If you are the only administrator and have no backup sign-in methods registered, you will need to find a secondary 'break-glass' admin account credential. If one is not available, you must contact Microsoft Support and provide your request and correlation IDs to regain access.

What should I do if removing the account from the app doesn't work?

If re-registering the account in Microsoft Authenticator does not resolve the issue, try using the 'Other ways to sign in' link on the login screen to use a backup verification method like an SMS code or email link. Alternatively, an admin must reset your MFA profile entirely.

Login & Account Issues