I’d say there’s likely something wrong with your service. Maybe it refuses serving on a domain it’s not configured for? Or there’s something wrong with the headers or something like that. Or the internal network. Anyway, the 502 error is sent by the Caddy server. That means everything from your browser to the Caddy server should be fine. You can reach it. There’s something wrong with the service or the parts in-between the reverse proxy and the application.