Fix a 400 Error When Connecting Microsoft Foundry to Copilot Studio
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A Microsoft Foundry agent can return a 400 error in Copilot Studio when its endpoint lacks Activity Protocol support. A trailing slash may resolve it.
Original article from September 7, 2026: Fix 400 Error While Using Microsoft Foundry to Copilot Studio, on Blog about anything related to my learnings. Read the original
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TL;DR
A Microsoft Foundry agent connected to Copilot Studio can return a 400 error when its stable endpoint does not support the Activity Protocol. Newly created agents typically expose Responses by default. Appending a trailing slash to the project endpoint may fix the connection; otherwise, check the agent endpoint protocol configuration.
Why it matters
- Makers: Append a trailing slash to the Foundry project endpoint and retry, because the source reports this may remove the 400 error.
- Makers: Check whether the stable Foundry agent endpoint supports the Activity Protocol, because Copilot Studio requires that protocol for the connection.
Frequently asked questions
What does endpoint does not support activity mean in a Copilot Studio and Microsoft Foundry connection?
It means Copilot Studio is calling the Foundry agent through the Activity Protocol, but the agent endpoint is not configured to support it.
Can adding a trailing slash fix the Microsoft Foundry project endpoint 400 error in Copilot Studio?
Yes, appending a trailing slash to the project endpoint may make the 400 error disappear. If it does not, inspect Activity Protocol support.
Which protocol must a Microsoft Foundry agent endpoint support for Copilot Studio?
The stable Foundry agent endpoint must support the Activity Protocol. Newly created agents typically expose Responses by default, so other protocols may need configuration.