I heard from a reader who was having trouble purchasing a book on the Kindle app for her iPhone. “Amazon is only letting me progress as far as to put them on a list, but I can’t seem to purchase? What am I doing wrong?”
Have you purchase books directly from your Kindle app on the iPhone before. If not, it’s possible you don’t have in-app purchases turned on for your Kindle app. If you have purchased before, it’s possible that something has changed about your credit card information since the last time you made a purchase from the phone. Perhaps it expired?
If neither of these turns out to be the case, I’d suggest uninstalling and reinstalling the app.