The new app update no longer accepts a credit card purchase of a book. Instead, the only method for buying a book is with a credit. My monthly credit is of course free with my subscription, but to buy another book requires a purchase of an additional credit. In other words, if I want to purchase a $4 book, I now have to spend $33 to buy 3 credits, so my $4 book just cost me $11. Don't bother trying to circumvent this by buying direct from Amazon; you can't.