In fact, you’re free to’t purchase them from the Amazon app either.
Even if you’re an Amazon Prime member and you want to download a free book.
Nah, not possible.

The App Store was introduced in July 2008 with the release of “iPhone OS 2.0”.
Being forced to price-match in-app sales while paying Apple’s 30% commission proved challenging for many businesses.
Use Safari or Chrome mobile web online window and useAmazon.comto complete your purchase.
Then go back to the app.