A 502 Bad Gateway from Caddy means that when you tried to connect to localhost:2020, Caddy tried to proxy your request to http://10.0.0.251 (or .252 or .253) but wasn’t able to establish a connection.
You’ll need to troubleshoot why those endpoints aren’t accepting HTTP connections. Start by using curl -i http://10.0.0.251 from your Caddy host, which will give you a good idea of exactly how that backend is (or isn’t?) responding to Caddy.