As I edited above, it looks like Amazon changed this (or maybe it was always like that since I always use the website). According the Apple documentation though, a user should be allowed to bypass IAP for purchases that will be consumed outside the application. See:

https://developer.apple.com/app-store/review/guidelines/#in-...

https://developer.apple.com/app-store/review/guidelines/#phy...

Admittedly it has been a few years since I was deeply in iOS development dealing with this.