Apple announced that it is now offering developers the ability to create promo codes for in-app purchases. By doing so, it gives them a simple way to allow testers, reviewers, and journalists access to app content that would normally only be available after purchase.
Developers could provide promo codes to download their paid app for free, but they couldn't provide paid content in the app without the need for "in-app" additional purchase. This changes.
Developers can donate 100 promo codes for each paid item that is available for purchase in their app and maxat least 1 promo codes per month.
Source: macrumors