Did you read server documentation?
One special thing is that if you configured the printer, the server will always connect to printer and host can not connect any more (unless you deactivate the printer in server to free port).
If you choose to run it over the server, you do not use the serial connection any more (cause it is blocked). You need to choose the server connector in printer settings, so you communicate through the server now. Only then do you get the advantages of both - the server and host.