you only pay royalties if you make more than a certain amount each quarter, im pretty sure that amount is $3000. Idk what gamejolt is but if its some kind of app store or something, youre fine. If its something like kickstarter, thats a little different. In the latter case, you owe epic a percentage from donations you get based on access to their software Ex: donate $20, get a free tshirt, donate $50 you get a free tshirt and a free copy of the game, you owe epic 15%(not sure if that number is right) of $30 because the amount they donated specifically for their software was $30.