The prohibition of “PSIKA” forbids paying for a purchase in advance of receiving the item purchased if the seller will not charge the buyer more in the case of a price increase at the time of receipt of the product purchased. The actual pre-payment is forbidden, even if no eventual price increase occurred. Thus, why is it permitted to purchase a lottery or raffle ticket in advance of the drawing time, being that the purchaser receives nothing at the time of purchase? (The ticket itself is not the item purchased, it is rather just a record of his payment to enter the lottery or raffle at the time of the drawing).
The purchaser did receive something at the time of purchase- the chance of winning the lottery. This is something that is worth money at the time of the sale, and it does not increase with time. Whether he receives the actual ticket or the rights to win the lottery, it is still a sellable commodity that has a steady price, therefore it isn’t psika and permitted.
Bris Pinchos 17-42.