Connection Error - Check if your MCP server is running and proxy token is correct

[deiu]

Inspector Version

• v0.16.8

Describe the bug
I am trying to connect to a custom MCP server (standards compliant). The MCP proxy seems to connect successfully (getting HTTP 200 from the proxy) but the UI still displays Connection Error - Check if your MCP server is running and proxy token is correct and I cannot interact with the MCP server.

Is there any way to enable more debugging on the poxy side?

Browser request (proxy API):

Request URL: http://localhost:6277/mcp?url=http%3A%2F%2Flocalhost%3A3001%2Fmcp&transportType=streamable-http
Request Method: POST
Status Code: 200 OK
Remote Address: [::1]:6277
Referrer Policy: strict-origin-when-cross-origin

Terminal logs (proxy API):

New StreamableHttp connection request
Query parameters: {"url":"http://localhost:3001/mcp","transportType":"streamable-http"}
Created StreamableHttp client transport
Client <-> Proxy  sessionId: ab929992-4e49-42f3-8781-dffe3ba73c8c
Proxy  <-> Server sessionId: 12296ebda72c5222f364de889c4a52a8

Expected behavior
Inspector connects to the MCP server and allows me to inspect the server's features.

Screenshots

Environment (please complete the following information):

• OS: macOS
• Browser: Chrome

Additional context
Add any other context about the problem here.