Error 500121

Question

Error 500121

Keith levy 0

why is my authenticator is sending me the code and after i verify, it send a second code that does not allow me to verify and then an error message 500121?

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2 answers

Your answer

Answer 1

Error 500121 means Microsoft Entra did not receive a completed multifactor authentication (MFA) response; use another registered verification method if available, then replace the Authenticator registration that is generating repeated prompts.^1^

Work or school account

On the sign-in page, select Sign in another way or Other verification options.
Use an already registered method, such as SMS, phone call, or security key.
Once signed in, open https://mysignins.microsoft.com/security-info.
Select Add sign-in method and register Microsoft Authenticator again.
After confirming that the new registration works, remove the old Authenticator entry.^2^

If you cannot sign in with another method, contact your organization’s help desk and request an MFA re-registration. Send these instructions to an authorized Microsoft Entra administrator:

Open Microsoft Entra admin center.
Go to Entra ID → Users.
Select the affected user.
Open Authentication methods.
Select Require re-register multifactor authentication.
Have the user sign in again and complete the Authenticator setup through to the end.^3^

Do not perform the administrator reset yourself unless you are an authorized administrator with access to the tenant.

If you are the only Global Administrator and are completely locked out, there is no second administrator available to reset MFA. Contact Microsoft customer service and request a tenant-access case for the Data Protection team.^2^

Personal Microsoft account

The Entra administrator reset does not apply to a personal account. Try another verification option connected to the account. If none works:

In Authenticator, open the top-level menu.
Select Send feedback to submit diagnostic logs.
Contact Microsoft Support or use the Microsoft Authenticator forum, including the error code and timestamp but excluding personal identifiers.^4^

If the prompts continue after re-registration

Check these items before trying once more:

Unlock Authenticator before responding.
Enable Authenticator notifications.
Update Authenticator to the latest version.
Set the phone’s date and time to automatic.
Switch between Wi-Fi and mobile data if connectivity is unstable.
Avoid making many repeated attempts; repeated work/school sign-ins may temporarily prevent further attempts.^5^^6^

An administrator can diagnose persistent failures under Entra ID → Monitoring & health → Sign-in logs. Filter by the user and failed status, then inspect Failure reason and Additional Details for the 500121 event.^1^

References

Answer 2

Hi @Keith levy,

Error 500121 means the multifactor authentication (MFA) request could not be completed. The second verification prompt may have expired, been rejected, or your Microsoft Authenticator registration may no longer match the account.

First, please try signing in again and select Sign in another way if another verification method is available.

If no other verification method is available and your account is an end-user account, please contact your organization's IT administrator.

Ask your administrator to revoke your existing MFA sessions and require MFA re-registration. They can follow the guidance here: Manage authentication methods for Microsoft Entra multifactor authentication

User's image

This process removes previous sign-in sessions and forces a fresh MFA registration. It often helps resolve Error 500121 when existing authentication data is no longer synchronized with the account. The next time you sign in, you'll be prompted to set up Microsoft Authenticator again from scratch.

If you are an administrator, please check whether another administrator in your organization can reset MFA for your account using the steps above.

If you are the only administrator, please contact Microsoft Support directly by phone: Contact Microsoft customer support

In this situation, the Microsoft Data Protection team has tools and processes in place to verify identity and regain access to administrator accounts.

Here are some tips and an example of a prompt to help you navigate the IVR more effectively:

(When you call the support number, you may hear an introduction of about 30 seconds such as "you can visit the link...". You can ignore this introduction and wait until you are presented with the options. Then press "1" as a business email user, and again "1" for technical help.)

In some regions, the initial interaction may be automated, so here’s a general idea of how the conversation might go to help you prepare:

What kind of problem are you experiencing?

Answer: Authenticator

What products do you use?

Answer: Office 365 for business

Is this for an education or company account?

Answer: For companies

Are you an administrator?

Answer: Yes

Are there any other administrators in your organization?

Answer: No. I am the only admin in my tenant

Do you need a... Service request?

Answer: Yes. I need to create a ticket. Please send me direct to the Data Protection Teams.

During the phone call, you will need to provide the information associated with your subscription, such as your company name, billing details, phone number, and an alternate email address, etc. This information allows the Data Protection team to verify your identity and securely assist you in regaining access to your administrator account.

I hope these suggestions help you find the appropriate solution for this issue. Thank you so much for your understanding.