MFA & Verification Issues

Fix Microsoft 365 Sign-In Fails With Authenticator JSON Error

Rana Garcia Oct 13, 2026 868 views

Question details

The user is unable to complete the Microsoft Authenticator setup for Microsoft 365 due to a SyntaxError involving JSON.parse, which loops the sign-in process back to the initial screen.

How to Fix Microsoft 365 Sign-In JSON Parsing Error in Authenticator

Product: Microsoft 365
Device & OS: not provided
Scenario: Setting up multi-factor authentication (MFA) or signing into Microsoft 365 using the Microsoft Authenticator app.
Observed behavior: The authentication process fails with a JSON parsing error and returns to the initial sign-in screen. The issue persists even after adding a security key, clearing browser cache, and switching to different devices.

Before you start

Ensure you have your Microsoft 365 administrator's contact information handy, as persistent authentication errors often require backend account resets.

Solution 1Recommended

Reinstall Microsoft Authenticator and Use a Private Browser

Corrupt app data or cached browser tokens can cause JSON parsing failures. Performing a clean installation and using an incognito window helps bypass local data corruption.

A JSON parsing error often means the authenticator app is receiving an unexpected or malformed response from the authentication server. Clearing all local configurations forces a fresh connection.

Uninstall the Authenticator App

Remove the Microsoft Authenticator app from your mobile device completely to wipe existing corrupted data.

Reinstall the Application

Open your device's app store (Google Play Store or Apple App Store), search for Microsoft Authenticator, and install the latest version.

Open a Private Browsing Window

On your computer, open a private or incognito window in your web browser (e.g., Ctrl+Shift+N in Chrome or Edge) to prevent old cache from interfering.

Restart the Setup Process

Navigate to the Microsoft 365 sign-in page in the private window and follow the prompts to register your new Microsoft Authenticator installation.

Reinstall Microsoft Authenticator and Use a Private Browser

Account Re-registration: Uninstalling the app will remove your existing MFA tokens. You will need to re-register any other accounts you previously had in the authenticator.

Solution 2

Contact Your Microsoft 365 Administrator

If the error occurs across multiple browsers and devices, the problem is likely tied to your account's provisioning status on the server side.

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Frequently Asked Questions

What causes a JSON parsing error in Microsoft Authenticator?

This error typically occurs when the authenticator app receives an invalid, corrupted, or incomplete response from the authentication server. It can be caused by outdated app versions, corrupted browser cache, or server-side account provisioning glitches.

Will clearing the Microsoft Authenticator data delete my other accounts?

Yes. If you clear the app data or uninstall Microsoft Authenticator, all saved accounts and MFA tokens will be erased from your device. You will need to re-add them using your backup authentication methods or recovery codes.

Why does the Microsoft 365 sign-in error happen on all my devices?

If the exact same error appears across multiple computers and mobile devices, it confirms the issue is not with your local hardware or cache. Instead, it indicates a problem with your account's configuration on Microsoft's servers, which must be resolved by your IT administrator.

Login & Account Issues