could you see the reason it didn't work?

It's been a number of years, and all I really remember is coming to the conclusion that "emacsclient only works with a local server." It uses a domain socket for this, but forwarding that from a remote server doesn't seem to be enough.

Simply editing a remote file over an ssh connection is easy enough using TRAMP, but that isn't the same as accessing existing buffers in a remote server.