In order to sell a single issue on your Android app, you need to create the corresponding product ID on Google Play.
Follow these instructions to create and submit all the product IDs you need:
1) Open your Google Play dev account (https://play.google.com/apps/publish/)
2) Select your app and click on "in-app products"
3) Select "Managed product"
4) Product ID: You can find your product ID on Paperlit Dashboard. In the issue details, click on the "Show product IDs" button.
5) Enter the price and flag "Replace all the prices"
6) Select "Active" from the drop menu' on the top of the page
The product will go live immediately.