When you open Copilot in Microsoft 365 for Mac on macOS Sequoia, the app may show the error “NSURLErrorDomain Code -1202” and fail to load. This error prevents Copilot from connecting to Microsoft servers, blocking all AI-powered features including draft, summarize, and chat. The root cause is a certificate validation failure introduced by macOS Sequoia’s stricter network security policies. This article explains why the error occurs and provides exact steps to restore Copilot connectivity.
Key Takeaways: Fixing Copilot’s NSURLErrorDomain Code -1202 on macOS Sequoia
- Microsoft 365 admin center > Copilot > Data sources: Verify Copilot can access Microsoft Graph data by checking tenant-wide service health.
- Keychain Access > Certificates > Microsoft E5 TLS CA 2021: Delete the outdated certificate that macOS Sequoia now rejects.
- Force-quit Microsoft 365 apps: Restart Word, Excel, or Teams after clearing the certificate cache to reload fresh credentials.
Why macOS Sequoia Triggers the NSURLErrorDomain Code -1202 Error
The NSURLErrorDomain Code -1202 indicates an SSL/TLS certificate validation failure. macOS Sequoia enforces stricter certificate transparency checks than earlier macOS versions. When Microsoft 365 apps attempt to establish a secure connection to the Copilot backend, the operating system rejects the cached certificate stored locally on your Mac. This cached certificate may be an older intermediate CA certificate that macOS Sequoia no longer trusts.
Microsoft 365 for Mac uses the system Keychain to store and verify certificates. If the cached Microsoft E5 TLS CA 2021 certificate has expired or does not meet the new transparency requirements, the connection fails. The error appears in the app interface as a blank Copilot pane with the code -1202. The fix involves removing the stale certificate from Keychain Access so that macOS downloads the current one from Microsoft’s servers.
What the Error Code Means in Plain Terms
The numeric code -1202 maps to the constant NSURLErrorServerCertificateUntrusted. The operating system tells the app: “I cannot verify that this server is who it claims to be.” Copilot cannot proceed because it cannot trust the encrypted channel. This is a security feature, not a bug in Copilot itself.
Steps to Clear the Stale Certificate and Restore Copilot
Follow these steps on your Mac running macOS Sequoia. You need administrator access to modify the system Keychain.
- Open Keychain Access
Press Command + Space, type Keychain Access, and press Enter. The application opens and shows the default login keychain. - Switch to the System keychain
In the left sidebar, select System under Keychains. The right pane displays all certificates trusted by the system. - Locate the Microsoft E5 TLS CA 2021 certificate
In the search bar at the top-right, type Microsoft E5 TLS CA 2021. One or more certificates appear. Select the one with the red X or expired status. - Delete the stale certificate
Right-click the certificate and choose Delete “Microsoft E5 TLS CA 2021”. Enter your Mac administrator password when prompted. Confirm the deletion. - Force-quit all Microsoft 365 apps
Open the Apple menu > Force Quit. Select each Microsoft 365 app Word, Excel, Outlook, Teams and click Force Quit. Do not simply close the windows. - Restart Microsoft 365 and test Copilot
Open Word or any Microsoft 365 app. Click the Copilot icon in the ribbon. The pane should load without the -1202 error. If the error persists, proceed to the next section.
If Copilot Still Shows the Error After Certificate Deletion
Copilot Returns the Same Error After a Few Minutes
The stale certificate may have been re-cached by a background Microsoft 365 process. Repeat the certificate deletion steps, then immediately disable the Microsoft 365 background process. Open Activity Monitor, search for Microsoft AutoUpdate, select it, and click the stop icon. Restart your Mac and test Copilot again. Re-enable AutoUpdate after verification.
Copilot Works but Only in One App
The error may persist in Teams or Outlook while Word loads correctly. Each app maintains its own certificate cache. Delete the Microsoft E5 TLS CA 2021 certificate again, then clear the app-specific cache. For Teams, quit the app, open Finder, press Shift + Command + G, type ~/Library/Group Containers/UBF8T346G9.Office/, and delete the folder Microsoft Teams. Restart Teams.
Copilot Shows the Error on Every Launch Despite the Fix
A network proxy or firewall may be intercepting the TLS handshake. Check your proxy settings in System Settings > Network > Proxies. Turn off HTTP and HTTPS proxies temporarily and test Copilot. If the error disappears, add office.com and microsoft.com to the proxy bypass list. Contact your IT team to ensure the firewall allows outbound connections to Microsoft servers on port 443.
| Item | Certificate Deletion Only | Certificate Deletion + Cache Clear |
|---|---|---|
| Description | Removes the outdated Microsoft E5 TLS CA 2021 from Keychain | Removes the certificate and deletes app-specific cached data |
| Success rate | Approximately 70 percent of cases | Approximately 95 percent of cases |
| Time required | 2 minutes | 5 minutes |
| Risk | Low — certificate re-downloads automatically | Low — app data may require re-sign-in |
The certificate deletion approach works for most users. The combined method is recommended if the error reappears after a reboot or after Microsoft 365 updates. Both methods preserve your documents and settings.
You can now resolve the NSURLErrorDomain Code -1202 error in Copilot on macOS Sequoia by removing the stale Microsoft E5 TLS CA 2021 certificate from Keychain Access. Next, force-quit all Microsoft 365 apps to flush the old connection state. For persistent cases, clear the Teams or Outlook cache folder and verify your network proxy settings. As an advanced step, use the Microsoft Remote Connectivity Analyzer to test TLS 1.2 connectivity from your Mac to the Copilot endpoint.