Oh wow, had no idea this was a thing but apparently it's an itch restriction, so I can't really do much about it. I guess you'll still have to pay $1 manually.
Kind of a bummer tbh that the game can't really participate in sales for this reason (which is actually also the case on Catalog where $1 is a hard minimum, so I'm thinking about raising the price for that reason alone, which is also annoying...).