Just rented a server and when I try to start, it goes online for probably a solid second, then goes back offline.
Well first thing to know is that once you rent a game on your server, it becomes active almost immediately from G-Portal on your server. However, it can take up to a couple of hours for the game to sync fully with the developer on the backend.
If you wait for more than 2 hours and are still not able to connect or start the game, you will want to go into Support and do the Write a Ticket thing so G-Portal will then have permission to approach the dev of the game and sort out connections.
I'm having the same issue but I need to update it