No problem. And yeah, sorry about that. It's a default Listia setting. I'm not sure exactly how it chooses what can and can't be bid on, but it's sort of a system to keep people from signing up, bidding on something, winning, then leaving. Sellers can't do anything to change it.
Correction, I forgot this listing was for the LINK, not the KEY. What happens is you follow the link, input your email (it's a Humble Bundle link), and that sends you the key.