The minimum is 4 slots. You can pay for 4 slots, if you only have 3 and cannot find another player to play with, and they will glady facilitate your game.
You only pay for the three. Depending on the number of people that is maximum for the room you want to play they put other people with you. B for example if you are wanting to play in a room that maximum is 6 they will put 3 other people that want to play with you.
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