You can no longer make in-app purchases from Amazon's Audible, Kindle, and Music apps on Android
If you use Amazon's Audible app on Android to listen to audiobooks while you do your cardio, you may have noticed that you can no longer buy audiobooks directly from within the app. Don't worry, this is not a bug. Amazon no longer offers in-app purchases from its Audible, Kindle, and Music apps on Android (via Engadget). The only thing you can now buy is credits from the Audible app.
Amazon has begun sending notifications to its customers, so you may have received an email from the company explaining what is going on and why it needs to make this change. Long story short, Google decided to follow Apple's example and has begun enforcing a new rule requiring all apps that have been downloaded through the Play Store to process payments for "digital goods and services" through the Play Store billing system.
Another solution, as pointed out by Android Police, is that instead of going to Amazon's website, you can download the Amazon Appstore App for Android. There you will have access to different versions of the Amazon apps, which support in-app purchases. However, you will need to uninstall the apps from the Play Store first before installing the Amazon Appstore App.
If Amazon hadn't introduced the change, Google's rule would have meant that Big G would earn a cut from your next purchase on the Audible, Kindle, and Music apps on Android. It looks like Amazon doesn't want Google to take a percentage of its profits, so this is why next time you want to buy something from Amazon's services, you have to use the company's website to make your purchase.
Another solution, as pointed out by Android Police, is that instead of going to Amazon's website, you can download the Amazon Appstore App for Android. There you will have access to different versions of the Amazon apps, which support in-app purchases. However, you will need to uninstall the apps from the Play Store first before installing the Amazon Appstore App.
Things that are NOT allowed: