@tce it’s not client-side error, openai have the same error on the website :
https://platform.openai.com/playground/prompts?models=gpt-4.1 → you can add your MCP endpoint.
Then three possibility :
- it’s error in MCP server
- protocol openAI MCP don’t accept FastMCP
- the streamable-http is in WIP
maybe could work with old FastMCP version I didn’t try
(Update 3 hours later this post) :
I change some redirect config from my Apache2, to handle SSE,
Because Http contain SSE and JSON, then check if you redirect the SSE request to your port of your service. My certificate was already good.
Good luck other dev, I stay online to answer questions if needed.