A Mystery game is a special round, but you still have to pay for it. Therefore, you need credit to play your Mystery game.
A Mystery game must be played with the same stake that was used to win it. For example: if you win a Mystery game with a stake of €5, you must play it with a stake of €5.
If you won your Mystery game with a stake of €20, but you only have €5 game credit left in your tournament, you unfortunately don’t have enough credit to play your Mystery game.