Microsoft Authenticator

Question

Authenticator wont sign me in without approval from authenticator. Continuous loop and error code 500121

Answer 1

Hi @Kelly Segal

The repeated approval prompt in Microsoft Authenticator with error code 500121 usually means there’s a stuck or invalid sign‑in session in Microsoft Entra ID. Because of this, the authentication never completes and results in a continuous loop.

If you’re 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.

They can follow these steps:   

1. Sign in to the entra.microsoft.com as at least Authentication Administrator.   
2. Select User -> All user.   Select the user (your account) to act on and select Authentication methods. then select Require re-register of multi-factor authentication.    

• Require re-register MFA: This disables all previous authentication methods. You'll then be prompted to configure a new MFA authentication method the next time you try to sign in, so you can set up from the start and add a new authenticator app.   

 

For more details, please refer to: Manage user authentication methods for Microsoft Entra multifactor authentication. 

Note: Once re-registration is triggered, all your existing MFA methods such as phone numbers, Authenticator app, or other verification options will be removed. You will need to set up new MFA methods during your next login. Please ensure you have access to a valid phone number or the Microsoft Authenticator app before attempting to sign in again. 

If you are the only global administrator and is locked out, the next step would be to contact Microsoft Data Protection team directly for assistance as they have tools and processes in place to verify identity and regain access to administrator accounts.      

You can find the appropriate customer service phone numbers at this link: Customer service phone numbers.

Please remember to provide them with your account details and explain the situation. Be ready to provide:     

• The company name used during subscription    
• Billing email address (even if it’s a personal Microsoft account)    
• Payment method details (last 4 digits of the card, billing address)    
• Any subscription ID or invoice numbers from billing email    

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.

To make the process smoother, here’s an example of how to respond when speaking to the automated system (IVR):     

IVR: What kind of problem are you concerned about?     

You:  Authenticator.    

IVR: What kind of product do you use?     

You: Office 365 for business.     

IVR: education or company account?     

You: For companies     

IVR: Are you an administrator?     

You: Yes.     

IVR: Do you have the other administrator in your organization?     

You: No.     

IVR: Do you need a... Service request?     

You: Yes     

These prompts help direct your call to the right support team more quickly, especially when dealing with account lockouts and authentication issues. 

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. This would allow you to create a new tenant following the provided prompts.    

• Follow the guided setup to create a new Microsoft account and a new tenant.
• This tenant will be completely separate from your existing Microsoft 365 environment.

Once set up, you can access the admin console of the new tenant by logging into admin center and follow the steps in this article: Get support - Microsoft 365 admin and submit a support ticket requesting to speak with the Data Protection team on behalf of your previous tenant.    

Include the following details:

• The administrator email address for the locked tenant
• The domain name of the locked tenant
• Any error messages you are seeing
• A description of the authentication or sign‑in issues
• Confirmation that you are the administrator of the locked tenant

Before submitting the ticket, make sure the Support Assistant is turned Off as several customers have reported that when the Support Assistant is enabled, the Contact Support option may not appear.

As shown in the screenshot, simply switch Support Assistant > Off, then enter your issue description. Once disabled, the Contact Support button should appear, allowing you to submit the ticket normally.

Important note:

• This new trial tenant does not provide access to any data, users, or settings from your original locked tenant. It is only intended as a temporary way to contact Microsoft Support.
• Once the issue with your original tenant is resolved, be sure to cancel the trial subscription to avoid any unintended charges. You can do this from the Microsoft 365 Admin Center by going to Billing > Your products and canceling the trial there.

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

As forum moderators, we don’t have access to the detailed system needed to troubleshoot this effectively due to privacy and security constraints. To quickly resolve this and regain access, the most effective step is to contact Microsoft Support Team directly. Only they have the ability to help with your Authenticator issue.    

Hopefully it will help work with your issue and if you have any other questions or need further assistance, feel free to ask.   

---

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 2

Error 500121 with Microsoft Authenticator usually means the sign-in cannot complete because the required authentication step never finishes, which causes the loop.

Try these steps on the device with Microsoft Authenticator installed:

1. Open Microsoft Authenticator directly and make sure it is unlocked
   • If the app is locked, unlock it first; the approval prompt may not show while it is locked.
2. Check notifications
   • Ensure notifications for Microsoft Authenticator are enabled and not set to silent.
   • Then retry the sign-in so a new prompt is sent.
3. Update the app
   • Make sure the latest version of Microsoft Authenticator is installed from the app store.
4. Check network and device settings
   • Confirm the phone has internet access; if needed, switch between Wi‑Fi and mobile data and try again.
   • Verify the device date and time are set correctly (automatic time is recommended).
5. If the sign-in still cannot complete
   • If there is another authentication method configured (SMS, alternate email, etc.), use that to sign in and then review or reset the Authenticator setup.
   • If there is no alternative method and this is a work or school account, contact the organization’s IT admin and ask them to reset MFA or require re‑registering multifactor authentication for the account so Authenticator can be set up again.
   • If this is a business tenant where the affected account is the only admin and no other method works, contact Microsoft support by phone and request the Data Protection team to help reset the authentication methods, as described in the referenced Q&A guidance.

If the password itself is no longer known, use the password reset flow: Reset your password.

---

References:

• Authentication did not complete
• Troubleshoot problems with Microsoft Authenticator
• Authenticator Did Not Complete Login
• How to add your accounts to Microsoft Authenticator
• Microsoft authenticator sending me into a spiral - Microsoft Q&A
• 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
• I need to reset my mfa methods - Microsoft Q&A
• Requesting a Tenant Admin MFA Reset - Microsoft Q&A