itch.io

It is the honour system, the purchase button gives you the donate link.

He must have temporarily removed it, but Michael added an info screen for the shop; you're supposed to click "Purchase", and it will direct you to Albert's donation page, and they ask that you pay $1 before using a skin in game, but there's no in-game check for the transaction, it's just the Honor System

most likely this will be brought to steam where you actually have to buy the skins. so the effort is worth it