Everything else I've bought on itch was purchasable with just my card, no billing info required.
Viewing post in What's So Cool About Magic Portals? comments
Hey, I realise this thread is old, but maybe this info will be useful for someone: You have to enter an address if there is a minimum price set. If it's "pay what you want", including you can pay nothing, you don't. My best guess is that's because with a minimum price, itch.io may be required to charge VAT, depending on the buyer's location, but if the product is free, what one pays is considered a tip and doesn't have to be taxed