Anyone else hitting 424 / TaskGroup errors when creating a custom MCP connector?

API Bugs
1

Hi all,

I’m experimenting with MCP connectors in Developer Mode and ran into something odd.

When I try to add a custom MCP connector, the ChatGPT UI fails with a 424 error:

{“detail”:“unhandled errors in a TaskGroup (1 sub-exception)”}

On my side:

  • My MCP server is public and healthy.

  • It responds correctly to initialize, tools/list (with both “search” and “fetch”), and tools/call.

  • Responses are valid JSON-RPC 2.0 and match the MCP docs.

  • Curl checks all return 200 OK.

  • Logs show no new requests at the moment the 424 appears, so it seems to fail in the validator before hitting the server.

Has anyone else seen this recently? Curious whether this is a known validator issue or if there are hidden handshake requirements not in the docs.

Thanks!

3 Likes
Getting "unhandled errors in a TaskGroup (1 sub-exception)" error when connecting/refreshing Development ChatGPT App
2

I’m having the same issue - did you ever figure out what was going on here?

3

+1. Did you figure it out?

2 Likes
4

Runnig into the same issue, testing around with the my mscp server. But surprisinglly the call to the mcp server was retried with identical params and then it succeeded. Could not find anything in the logs but the

mcp_protocol_error

424: unhandled errors in a TaskGroup (1 sub-exception)
5

Same here

{“type”:“http_error”,“code”:424,“message”:“424: unhandled errors in a TaskGroup (1 sub-exception)”,“is_error”:true}

MCP inspector returns results correctly though.

6

I solved this 424 issue after having it all day. I tried everything with chatgpt and what I learned is that this error means it can be anything. that’s why you will see a lot of solutions to this error and maybe none will work for you.

in my case it was the response my server was giving to the “initialize” method , that comes before the “tools/list” method. I had it but openai didnt like it for some reason.

here is the final vertion of the response to initialize:

return response()->json([ ‘jsonrpc’ => ‘2.0’, ‘id’ => $id, ‘result’ => [ ‘protocolVersion’ => ‘2025-03-26’, ‘capabilities’ => [‘tools’ => [‘listChanged’ => false]], ‘serverInfo’ => [‘name’ => ‘rosify-mcp’, ‘version’ => ‘1.0.0’], ], ], 200, [‘Content-Type’ => ‘application/json’]);

7

I’ve been struggling with this issue for several days, and it turns out the problem wasn’t in my code at all.
While inspecting the browser’s network traffic, I noticed something interesting:

Before showing the error message
{ "detail": "unhandled errors in a TaskGroup (1 sub-exception)" },
ChatGPT doesn’t even send a request to my MCP server.

Then, right afterward, I see another response:
{ "detail": "Must use workspace account for this operation" }.

For context, I’m a Plus user, and I started trying to add a custom MCP server after the Apps SDK was announced.