This is because you aren’t creating any sessions. Steam sockets were meant to work in conjunction with the sessions API. Given that right now you are using bits and pieces to create your own matchmaking, accessibility to the things you want isn’t as straight forward.
Creating a session via (ISession::CreateSession), waiting for its delegate to finish (ISession::OnCreateSessionComplete), and then calling GetResolvedConnectString would work on the host. Assuming Steam allows you to create sessions with our appId (you could try 480 instead of 212960).
That being said, if you have successfully created a netdriver with ?listen, you can go back to that original thread where you tried to get the net driver, ip and port, and it should be there on the host.