Last updated on August 29th, 2025 at 12:32 pm
Microsoft Authenticator Error 500121 is a frustrating roadblock that many users face when signing in to Microsoft 365, Microsoft Entra ID (formerly Azure AD), work, or school accounts. It typically appears when multi-factor authentication (MFA) fails during login.
This guide explains what the error means, why it happens, and provides a step-by-step troubleshooting process to help you get back into your account—whether you’re a regular user or the only admin locked out.
What Is Error 500121?
Error Code 500121 indicates that an authentication request was not successfully completed. It’s tied to strong MFA requirements in Microsoft Entra ID and usually occurs when:
- You deny or fail to approve an MFA prompt (e.g., tapping “Not me”).
- A Temporary Access Pass (TAP) has expired or was already used.
- Conditional Access Policies block sign-ins based on device, location, or risk level.
- Your Microsoft Authenticator app is outdated or misconfigured.
- Device time is not synchronized, causing one-time passcodes to be invalid.
Common Scenarios Where Error 500121 Appears
- You are asked for a code in Microsoft Authenticator, but the code never appears.
- You try to log into a new device, but your work/school account fails to authenticate.
- You are the only administrator and get locked out of your tenant.
- MFA resets or prompts never show up properly during login.
Step-by-Step Fix Error 500121
1. Sync Your Device Time
Time mismatches are one of the most overlooked causes of OTP failures.
- Go to Settings > Date & Time.
- Enable Automatic Time Sync and correct time zone.
- Restart your device and retry login.
Microsoft Authenticator codes are time-based (TOTP). Even a few seconds of clock drift can make the codes invalid.
2. Remove & Re-Add the Authenticator Account
If syncing time doesn’t help, re-registering the account often resolves the issue.
- Open Microsoft Authenticator app.
- Tap the account → Remove.
- On a PC, log in to your Microsoft account via the Security Info / MFA portal.
- Choose Add sign-in method → Authenticator app.
- Scan the new QR code to re-register.
3. Check Conditional Access & MFA Policies (Admin Only)
If you are an IT admin, check for policy or block issues:
- Go to Microsoft Entra Admin Center → Users.
- Select Multi-Factor Authentication from the toolbar.
- Review if your account is marked as Blocked.
- Check Conditional Access Policies to confirm that location, device type, or risk detection isn’t causing the lock.
If you or a user tapped “Not me”, Microsoft Identity Protection may have flagged the account and blocked it automatically.
4. Reset MFA Registration (If You’re Locked Out)
If you cannot authenticate at all:
- Ask your IT admin to reset your MFA registration.
- If you’re the only admin:
- Try signing in from a trusted device or location used before.
- If that fails, contact Microsoft Support with:
- Error Code: 500121
- Request ID, Correlation ID, and Timestamp shown on the error page.
- Microsoft may issue a Temporary Access Pass (TAP) or assist with account recovery.
5. Use Alternate MFA Methods (SMS, Call)
If the Authenticator app fails:
- Visit your Security Info page.
- Add a phone number or SMS method (if not already configured).
- During sign-in, select Other verification options to receive a text or call.
Note: Your organization must allow alternate methods in MFA policies.
6. Update or Reinstall the Authenticator App
- Check the App Store / Play Store for updates.
- If issues persist:
- Uninstall the Microsoft Authenticator app.
- Reinstall it and reconfigure using a fresh QR code.
7. Clear Browser Cache & Permissions (Web Logins)
If you’re stuck on a blank MFA prompt in the browser:
- Clear browser cache, cookies, and site data.
- Ensure JavaScript is enabled.
- Disable ad blockers or extensions that might block authentication pop-ups.
- Avoid private/incognito browsing when testing MFA logins.
What If You’re the Only Admin?
Being the sole administrator makes Error 500121 especially problematic. Here’s what to try:
- Sign in from a trusted device or network previously used.
- Use a backup method (phone number, SMS, or alternate email) if configured.
- Contact Microsoft Support with your error details (Code, Request ID, Correlation ID, Timestamp).
- Request a Temporary Access Pass (TAP) to re-register your MFA settings.
FAQs: Microsoft Authenticator Error 500121
Q. Is Error 500121 caused by Microsoft’s servers or my device?
Usually, it’s caused by local setup issues (time sync, misconfigured Authenticator, expired TAP). Rarely, it may relate to Conditional Access policies set by admins.
Q. Can I fix Error 500121 without reinstalling the app?
Yes. In many cases, simply syncing your device’s time or re-approving MFA fixes the problem.
Q. Why does Error 500121 keep coming back?
If your device frequently loses time sync or your MFA is misconfigured, the error may reappear. Always keep your Authenticator app updated.
Q. What should I do if I’m completely locked out?
If you’re the only admin, contact Microsoft Support with your error details to request recovery via a Temporary Access Pass.
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Error 500121 can feel like a complete lockout, but in most cases, it’s the result of time drift, outdated apps, or misconfigured MFA settings.
- Start with basic fixes like syncing your time and re-adding your account.
- If you’re blocked by Conditional Access or fraud alerts, work with your IT admin or Microsoft Support to reset MFA or unblock your account.
- To prevent future issues, keep your Authenticator app updated, back up your MFA settings, and configure alternate sign-in methods for emergencies.
With these steps, you should be able to restore secure access and avoid hitting Error 500121 again.
