M365 Copilot - Cowork cannot make a connection to custom MCP

Luís Teixeira 35 Reputation points
2026-05-13T13:20:25.58+00:00

Hello,

Within M365 Copilot app, I'm trying to connect to our custom Plugin which is a MCP but when I press connect it does nothing:
User's image

Neither on the App nor in the Browser.

Microsoft Copilot | Microsoft 365 Copilot | Development
Answer accepted by question author
Sayali-MSFT 6,396 Reputation points Microsoft External Staff Moderator
2026-05-15T08:50:53.7266667+00:00

Hello Luís Teixeira,
The issue where the “Connect” button does nothing in the M365 Copilot app but works in Teams is most likely caused by differences in how authentication is handled across Copilot surfaces. In most cases, the button triggers an OAuth flow that should open a browser or popup window, but in the M365 Copilot app this can silently fail due to blocked pop-ups, disabled third‑party cookies, or webview limitations. Since your setup works in Teams, it indicates the plugin and MCP server are configured correctly, but the authentication redirect or browser interaction is not completing in the M365 Copilot environment. This is often due to missing or mismatched redirect URIs (typically configured for Teams only), or browser/security settings preventing the auth window from launching or persisting session state.
Adjusting pop-up permissions, enabling cookies, and ensuring your OAuth app supports all required Copilot surfaces generally resolves the problem.

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