I've followed the quickstart for matchmaking and I've successfully gotten an IP address and port to connect to through GetMatch.
In the server, as far as I understand, I need to call RedeemMatchmakerTicket on AGameMode::Login in order to make sure the player should be there. There are two values to pass in RedeemMatchmakerTicket's request (LobbyID and Ticket) and I can't fully figure out which ones they are since those names don't show up in GetMatch's response.