Power Platform Community Forum Thread Details

Hi everyone,

I’ve registered an MCP Server with multiple tools and registered the MCP Tool in my agent in Copilot Studio. When the agent invokes the MCP tool directly, everything works as expected.

However, when I try to call the same MCP tool from inside a Topic flow, the tool appears under the Connector section (not under the Tools section). When the topic executes and attempts to invoke the connector action, the call fails with an HTTP 400.

Has anyone successfully invoked an MCP Tool from within a Topic Flow in Copilot Studio?
Do we need to explicitly configure or map input parameters for the MCP Tool in the Topic flow even though the tool schema is already defined on the MCP server?
How to map input parameters in the MCP Tool if that is causing the issue ?
For a 400 error in this scenario, what are the most common causes?
- Payload/JSON shape mismatch
- Missing required fields
- Incorrect parameter mapping
- Authentication/header issues
- Connector vs. MCP tool schema differences

Context

MCP tool works perfectly when invoked directly by the agent.

Fails only when called inside a topic via the connector.

Connector is automatically generated when MCP is registered.

Any insights, examples, or configuration guidance would be greatly appreciated!

Categories:

Calling actions from Copilot Studio

Topic creation & management

Model context protocol

Hello VG-04020555-0,

Here are concise answers and guidance for your scenario:

Has anyone successfully invoked an MCP Tool from within a Topic Flow in Copilot Studio?

Yes, but it requires correct parameter mapping in the Topic flow.

Do we need to explicitly configure or map input parameters for the MCP Tool in the Topic flow even though the tool schema is already defined on the MCP server?

Yes. Even if the schema is defined, you must map Topic variables to the MCP tool’s input parameters in the Topic flow designer.

How to map input parameters in the MCP Tool if that is causing the issue?

In the Topic flow, when adding the connector action, click on the action and map each required input to a variable or value from your Topic. Ensure all required fields are mapped and types match the MCP schema.

For a 400 error in this scenario, what are the most common causes?

Most common: payload/JSON shape mismatch, missing required fields, or incorrect parameter mapping. Less common: authentication or header issues (if it works directly, this is unlikely).