Error in Having Connection Issues while Making MCP in APIM

[AIS-Naman-Jain]

Issue Summary
Requests are reaching APIM, but fail with the error:

"reason": "ClientConnectionFailure", "message": "Client connection was unexpectedly closed.", "section": "outbound"
APIM Setup
SKU: v2 Premium

Network: VNet integrated with own subnet & NSG

Policies:

Inbound: Deny All (with allowed entries for devices and VNet)

Outbound: Deny All (with allowed entries for MCP backend APIs & devices)

APIM-to-APIM outbound: Explicitly Denied

Context
Using Expose REST API in API Management to act as MCP server. All relevant backend endpoints are allowed in outbound.

Suspected Cause
The MCP server process may perform internal APIM calls, which are currently blocked due to APIM-to-APIM outbound denial—this is the only restriction left.

Request
Please confirm if internal APIM calls are required by the MCP server process, and if so, advise on best practice to allow these secure.

[AIS-Naman-Jain]

Note their is no other issue with making the MCP server VIA apim , also from APIM logs VScode and other process can request the MCP server and its the outbound failing

[pitsnake69]

I am experiencing same issue. Did you ever get an answer on how to resolve this issue?

[AIS-Naman-Jain]

Yes , the answer and main issue is with using of Application insights ie when making a frontend response payload byte logging , so that make mcp to error out as while making call with SSE this make things go interfered and make process not work correctly and show this error.