Power Platform Community Forum Thread Details

I have created a custom connector called DoorLoopConnector in Make.PowerApps. After that, we created an action to get tenant data. When we test the API, it works fine and returns a status code 200.
However, the issue occurs when we connect this connector in Copilot Studio to retrieve data in the agent.
First, we create a new agent. After that, we add the DoorLoopConnector – getTenants action in the Tools section. Then we publish the agent.
When we enter the prompt “show all the tenant details”, the following error appears:
Error Message:
Evaluating PowerFx expression resulted in error while invoking the connector:
PVA.getTenants failed: JsonReaderException '<' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.
Error Code: ConnectorPowerFxError
Conversation Id: 0cabb15b-f541-474e-9fdd-6d23631ae22e
Time (UTC): 2026-03-12T11:03:40.184Z

Categories:

Calling actions from Copilot Studio

This error means your DoorLoopConnector’s getTenants action is returning data in a format that Copilot Studio (and Power Fx) does not expect. Specifically, the error:

JsonReaderException '<' is an invalid start of a value.

indicates that the connector is returning HTML (often an error page or login page), not JSON.

Why this happens:

When you test in PowerApps, you may be authenticated, so you get JSON.
When called from Copilot Studio, the connector may not be authenticated, or the API endpoint is returning an error page (HTML) instead of JSON.

How to fix:

Check Authentication:

Ensure the connector is set up with proper authentication (OAuth2, API key, etc.) and that Copilot Studio has access.
Re-authenticate the connector in Copilot Studio if needed.
Check API Endpoint:

Make sure the endpoint URL is correct and accessible from Copilot Studio.
Handle Errors in the Connector:

Update the connector’s definition to handle non-JSON responses gracefully, or ensure the API always returns JSON (even for errors).
Test in Copilot Studio:

Use the “Test” feature in Copilot Studio’s Tools section to see the raw response.