how do I fix a copilot error

Question

m365-copilot-app.m365copilot.errorPageTitlem365-copilot-app.m365copilot.serverErrorTitle(/): other side closedm365-copilot-app.m365copilot.errorPageText

Answer 1

You keep telling us this, but if many of us are having the issue... the problem is your update.

Answer 2

Dear @Alice Calmes,

I understand how disruptive it can be to encounter a server error like m365-copilot-app.m365copilot.serverErrorTitle(/): other side closed when trying to use Microsoft 365 Copilot. I can help you troubleshoot and resolve this immediately.

The core issue behind the "other side closed" error string is typically a session termination between your client application and the Microsoft backend servers. This can happen due to localized token corruption, cached network states, or transient service updates.

Depending on whether you are using Copilot on the web or via the desktop app, please follow the targeted repair guides below to restore your connection.

Option 1: If You Use Copilot via Web Browser

Corrupted session storage or blocked authentication tracking can cause the server connection to drop.

1. Clear Your Browser Cache: Press Ctrl + Shift + Delete (Windows), select your cached images and files for the past 24 hours, and clear them.
2. Allow Third-Party Cookies: Copilot requires cross-site cookie validation to confirm your M365 license.
   • In Microsoft Edge: Go to Settings > Cookies and site permissions > Manage and delete cookies and site data and ensure Block third-party cookies is disabled.
   • Try Incognito / InPrivate Mode: Launch a private window to see if a browser extension or a persistent cookie loop is forcing the server to close the connection.

Option 2: If You Use the Copilot / Microsoft 365 App

If the standalone app environment is corrupted, a localized reset will re-establish the connection.

• Repair / Reset the App: Go to Windows Settings > Apps > Installed Apps, locate the Microsoft 365 / Copilot app, click the three dots, and select Advanced options. Click Repair. If the error persists, click Reset to clear localized app data. . Please refer to this document: Repair an Office application - Microsoft Support
• Sign Out and Re-authenticate: Open any office app (like Word or Excel), click File > Account > Sign Out. Close all open windows, restart your device, and sign back in to force a fresh authentication token.  

Because this error reflects a dropped server response, it can occasionally be caused by an active service degradation or a temporary synchronization lag on your tenant's license.

• Run the Official Get Help Diagnostic: Open the Windows Get Help app, type Copilot connectivity troubleshooter or Copilot License Troubleshooter into the search bar and run the automated tool to identify backend blockages.
• Tenant Health Check: If you are in a corporate environment, please check with your M365 Administrator to verify if a service incident is actively impacting Copilot access in your region.

Please give these steps a try and let me know if your connection is restored successfully.

---

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

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 3

Use the available Copilot troubleshooters and basic connectivity checks to resolve this type of generic server error.

1. Run the Copilot connectivity troubleshooter
   • Open the Get Help app on Windows.
   • In the Search bar, enter Copilot connectivity troubleshooter.
   • Select it and follow the on-screen steps.
   • This troubleshooter checks for firewall rules or other blockers that could cause “other side closed” or similar server errors.
2. Check Copilot license status
   • If Copilot is not appearing or is intermittently failing, run the Copilot license troubleshooter:
     • Open Get Help.
     • In the Search bar, enter Copilot License Troubleshooter.
     • Follow the steps provided.
3. Verify network and browser settings (for web apps)
   • If the error occurs in a Microsoft 365 web app, ensure the browser allows third‑party cookies, which are required for Copilot license validation:
     • Microsoft Edge: Settings → Cookies and site permissions → Manage and delete cookies and site data → set Block third-party cookies to Off.
     • Google Chrome: Settings → Privacy and security → ensure Allow third-party cookies is selected.
     • Mozilla Firefox: Settings → Privacy & Security → under Enhanced Tracking Protection, choose Custom and ensure Cookies is unchecked.
     • Safari (macOS): Safari → Settings → Privacy → ensure Prevent cross-site tracking is unchecked; Advanced → ensure Block all cookies is unchecked.
   • After changing settings, refresh the page and retry Copilot.
4. If issues persist
   • For home users: after running the troubleshooters and checking cookies, contact Support from the Get Help app or via the support link in the Copilot help pages.
   • For business users: contact the Microsoft 365 admin to verify Copilot is enabled and not blocked by organizational policies; the admin can then open a support case with Microsoft if needed.

---

References:

• Copilot troubleshooters
• I am getting license validation errors with Copilot
• How to find and enable missing Copilot button in Microsoft 365 apps
• Copilot is missing, disabled, or doesn't work correctly