I was also getting the websocket error:
WebSocket connection to 'wss://...' failed: Error during WebSocket handshake: Unexpected response code: 400
After following @imit8r's suggestion and removing those lines it is all working!
Below is my nginx proxy conf if anyone else has the same issue. This is running on https behind Cloudflare on a subdomain using Cloudflare's DNS
and so far no problem.
Here is my options.json from the foundry/Config directory:
Thanks for setting this up @fithwum!