In-app purchases are individual purchases that are made within the app, although the app itself can be free. You can specify the price for a single issue in your iTunes Connect, Google Play, or Amazon Store account. At the same time as the price, you define a product ID there.
The product ID is a freely selectable identifier (eg, IssueMay2017) that allows your content to be monetised through the respective app stores.
To enter the product ID Into the Manger;
- Check 'Paid Content'
- Respecting product IDs from each App Store
- Select Save