The proxy to Home Assistant must have WebSocket support enabled.
Without proper configuration, Home Assistant will reject requests coming from a proxy with
400: Bad Request.
If the proxy server is a Docker container (e.g. Nginx Proxy Manager), the trusted
proxy must be the IP address assigned to the container by Docker. Add the following
http: use_x_forwarded_for: true trusted_proxies: - XXX.XXX.XXX.XXX # Docker IP of proxy server