ZKasino requires randomness for its games which it receives from an integrated Verifiable Random Function (VRF). A VRF is a Random Number Generator (RNG) that provides random outcomes which are verifiable on-chain. With a VRF, ZKasino is able to provide users provably fair outcomes that are impossible to have been tampered with. Chainlink VRF is the biggest VRF provider in crypto. More information on how a VRF like Chainlink VRF works, can be found here. For information on how ZKasino uses VRFs with its contracts, please see the Architecture page.
For VRFs to resolve RNG requests a lot of computation power is needed. Therefor, VRFs ask a fee to be paid for their efforts. The VRF fee is paid upfront by the user. Note that gas fees may seem high initially. This is because the VRF fee can only be calculated when the VRF request is made. A big portion of the VRF fee is refunded in the same transaction.
On their profile page a player can find "Pending VRF Requests". On very rare occasions the VRF request does not get resolved and the player's wager will be stuck in the game contract. After 100 blocks the player can click "Refund" to remove their wager from the game contract.