Socketio websocket not upgrading 403 error

Hi, I followed the fastapi traefik tutorial from here:, so I have the exact same config as in here Deploying FastAPI (and other) apps with HTTPS powered by Traefik - DEV Community

Everything works fine for the http part of the api, I have https.

But i'm also using python-socketio, and when i try to connect to the websocket endpoint, the https request get through, but I then get a 403 error instead of having the websocket upgrade.
I tried adding this label: traefik.http.middlewares.sslheader.headers.customrequestheaders.X-Forwarded-Proto=https to my fastapi service, it doesn't work.

I get the error: Firefox can’t establish a connection to the server at wss://...

Any idea how I can fix this ? Thank you