You must use 37.5k. There is 100% chance for jackpot every day after you spend that amount of coupons in event, so you can roll it every day for free power and coupons. That is some fair play from Oasis. We got on our server like 15 ppl (from 30 active), which everyone got it on that amount and not only once but every day.

Man. On our server everyone who spended 37.5k at one time (not 20k and after 10min again 20k, but at one try full 37.5k) everyone got 40k at that point. And every day. And it is not 1-2 ppl. It is like 15ppl so half of server. We had at this time no one, who didnt get it and spended that amount. All our whales at server already refunded money so they quit because when f2p which invested 0€ and played 10x less time overpowered someone who spended 1000€+ in only 3 days.. there is no reason to recharge in this game anymore.