Thanks for the info! I'm pretty sure you can pay <1$ for sales because it says so when you try to purchase the game.
From what I understand, when a project is <1$ during a sale, users have the option of adding more projects until the price is 1$ or above, alternatively they can tip the difference and pay 1$.
I’m not sure if that’s the case with all payment options, or only some of them, or if this is on certain regions only.