In-App Purchase: If you want to unlock features or functionality within your app, (by way of example: subscriptions, in-game currencies, game levels, access to premium content, or unlocking a full version), you must use in-app purchase. Apps may not include buttons, external links, or other calls to action that direct customers to purchasing mechanisms other than IAP.
Amazon Prime does this, no. In the Amazon iOS app, you can browse, but cannot buy items. You can still login using your Prime account.