There are a number of things you need to get right here. First, you need your own Steam app id. Next, you need to set the number public and private connections when you create an advanced session to the maximum players you want in a game, ensure use presence and should advertise is checked, while use LAN is unchecked. In find sessions advanced, best to set client servers only for the server types, unless you really are using dedicated servers. Then, you’ll need two separate Steam accounts on two separate computers to test your game, and both accounts need to reside in the same download region. And yes, this was a painful process of discovery.