Authenticator App not working. Can't sign in.

Hi @Michael Hatwik,        

Thank you for posting your question in the Microsoft Q&A forum.                

Regarding that you can't log in to your account due to Microsoft Authenticator. I’d like to ask a quick questions to better understand your situation and assist you effectively:      

Could you please clarify whether you are an end user or an admin?              

If you are an end user I would recommend you contact your account's Admin to reset your MFA settings through the Microsoft Entra Admin Center. Ask your administrator to follow these steps:    

1. Sign in to Microsoft Entra admin center with the admin account 
2. Go to Users 
3. Select the affected user account 
4. Open Authentication methods 
5. Revoke sessions 
6. Select Require re‑register MFA 
7. Save the changes               

Revoke MFA sessions and require re-register in the Microsoft Entra admin center                  

  Please note that forum moderators don’t have access to user accounts and cannot assist with actions such as password resets, login changes, or account recovery.  

You could provide your admin this article for a better view: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID |…              

If you’re unsure who the Global Admin is within your organization, you can find guidance on locating them here: How do I find my Microsoft 365 admin? - Microsoft Support.                 

Thank you again for your time and understanding. While my initial response may not resolve the issue immediately, I’d like to gather more details about your situation so I can assist you more effectively.              

I really appreciate your patience, and I’m here to help. Looking forward to your response!                  

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".               

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Because the account is a school (work or school) account and Microsoft Authenticator was removed and reinstalled, the multifactor authentication (MFA) registration on the account is now out of sync with the app. The result is that sign-ins keep asking for verification codes that never arrive, and there is no way to fix it from the user side without another working method or admin help.

Use these steps, in order:

1. Try all available verification methods

• On the sign-in screen, if there is an option like Use a different verification option or I don't have a code, select it and see whether:
  • SMS text, phone call, or email code is offered.
  • If SMS is offered but not received, check:
    • The phone does not block texts from unknown numbers.
    • The inbox is not full and the messaging app is working.
    • The number on the screen matches the last digits of the correct phone.
  • If email is offered, check the junk/spam folder for messages from @accountprotection.microsoft.com and mark it as a trusted sender.

2. Avoid repeated code requests

• Do not make excessive or repetitive requests for codes to phone or email, as this can trigger a temporary security block where codes are not sent at all.
• If many attempts were already made, wait and try again later, or use a different MFA method if one is available.

3. If no method works or no codes arrive

• For a school account, only the organization’s IT/admin can fully reset MFA when all verification methods are blocked or lost.
• Contact the school’s Help desk or IT administrator and explain:
  • The Microsoft Authenticator app was deleted and reinstalled.
  • No verification codes (app, SMS, email, or call) are being received.
  • Sign-in is blocked for all school resources.
• The IT admin should:
  • Check Microsoft Entra sign-in logs for blocked or unusual activity.
  • Reset or clear the MFA/authentication methods for the account so that registration can be done again on the current phone.

4. If the phone was lost or replaced

• If the device was lost or replaced (or effectively “lost” because the app was wiped), the standard resolution is:
  • Sign in using a different method (if any still works), or
  • Ask the organization’s Help desk to clear the MFA settings so that registration is prompted again at next sign-in.

5. For ongoing reliability

• Once access is restored, consider:
  • Adding more than one MFA method (Authenticator app plus SMS/phone/email) so there is a backup.
  • Optionally going “passwordless” (for example, using Authenticator notifications or other passwordless methods) as described in the documentation, which can reduce reliance on SMS codes.

If none of the above methods are available and there is no way to reach a school IT/admin, the account cannot be recovered through self-service alone because Microsoft support agents are not allowed to send verification codes or change security info for a school account.

References:

• Common problems with two-step verification for a work or school account
• Troubleshoot problems with Microsoft Authenticator
• Frequently asked questions about Microsoft Entra multifactor authentication