If you bought the game here on itch, why don't you juse download it here on itch? Why you going to that website that's dedicated only to users who bought the game a long time ago.
Not sure why it even does that, sounds like an itch thing tbh. If you can, DM me in discord (link to the server in the description) and I'll send you the link to the game while you're figuring out this itch thing.
