Best practice for waiting until a session is full before joining it?

The problem is that I don’t know how to communicate to the players when the game session starts. What I’m doing now is connecting the player to the session, then if the session has two players (meaning it’s full), then the player who just joined can start the session. Then, with an OnStartSessionComplete delegate, that player connects to the game. The problem is that OnStartSessionComplete only triggers for the player who locally started the game, meaning that the other player (the host) does not know when the game starts, so they can’t travel to the correct map to start it.