How do I join a free game?

Tap Join as usual: a free game opens the checkout too, with a price of 0, so you can see the game and confirm your spot. The only method is Pay host directly and nothing is charged. Online options stay visible but greyed out with “The game is free”. Tap the button at the bottom and you are in the game straight away.

In the same checkout you can bring friends and they join with you, and you can enter a referral code. Leaving a free game never costs money, because a late-cancellation fee cannot be higher than the price of the spot.