It is predetermined as said above. Yet I noticed and I find it kinda funny .. if you flip the middle card, treasure essence is always on the right. If you flip the right one it is always on the left and if you flip the left one it is always on the mid. Tbh they should just delete those flipping cards and just give the reward immidiately.

well yeah the prob is the less you play and less you spend the higher are your chances to get prizes to bait those who spend a lot on 0% win rate for them