To play the ''Knockout Challenge'' you must select and pay a stake. Players can either chose from a 5000 chips stake or a 10,000 one. The reward gets multiplied three or five times depending on your stake. 

Once the challenge begins, you should not quit it or you will lose your stake.  If you win all the three games you end up receiving your reward (depends on the stake amount). If you lose any of the games, you lose your stake and the challenge gets reset.