You probably need some extra TCP “servers” running on both machines. You’re certainly going to need the DDM server sunning :-
The TCP servers on the AS400 are the equivalent to TCP services. It’s also worth checking that you have a connection that works to the other machine using the location name, you can try pinging the location name :-
Or telnetting to the other machine :-
When you get to the signon screen press the attention key and use option 99 to return from the telnet session.