Others are having this problem too. I'm having a different issue. Check out this thread:
https://www.mobileread.com/forums/sho...d.php?t=115074
What I've found out: apparently the billing systems are talking to one another. In my instance, one timed out and declined my card. It sounds like one that lets you have the book is fine and the other that takes the money is not. Craziness. :/
PS - I love your choice of books! Vortex was pretty good and I'm obsessed with Hunger Games!