By following the reference they provided, which is to a post by the person running itch.io stating just that.
I don't know if the linked comment is actually correct, but the link to a comment plus quoteof the relevant part seems as factual as it gets.
Basically I didn’t notice the very slight indentation on my phone. Whoops.
I don’t know who sureglymop‘s registrar is. I’d encourage them to name and shame, refusing to refund is unacceptable.