Why not do what ravager did? Have this as a legacy version of the game that gives full updates to anyone who paid for the game, then make a separate standard version for the game AKA the free version so people who were willing to support before the itch bs can still play The paid version? And it does the filtering and fact checking for itself as itch knows who has and hasn't paid for the game so nobody is able to pretend they bought the game.
Edit: itch has made a way to purchase through itch, though it's only through PayPal and PayPal also allows for people to pay once off with a guest account and accepts both debit and credit cards.