I've seen that commonly, users try to use ws:// or wss:// either as site addresses or proxy upstream addresses. Neither of these work in Caddy, they're specific to browsers for use with the new WebSocket(url) JS API.

We should warn/error when those are used in the config, and suggest using http:// or https:// (or omitting the scheme) respectively.