Many people have received Amazon gift cards for Christmas and are itching to use them. Some people have run into the situation where they want to use their credits to buy audiobooks from Audible, after all Amazon owns them.
Amazon has a bug in their system that will not allow you to use Amazon credit to buy Audible books. Instead, it will just charge your credit card for the full amount and the audiobook will show up in your Audible account.
The same error happens if you visit the Amazon site to purchase the Kindle book and then add the audio for a reduced price. When this process is initiated it doesn’t redirect you to Audible, it just charges you for the full amount on Amazon.
Hopefully Amazon addresses this bug soon, because lots of people want to try an audiobook for the first time.