Developer Console Setup
To test your Android app for in-app billing, you need to log into your Google Play Developer Console. If you have not registered with Google as an app publisher, then you will, first of all, do that.
To create a new Google Merchant Account, go the Settings menu option inside your Developer console page. Then select Account details and scroll down to the bottom of the page. Click on Create merchant account button. Follow the remaining instruction to finish up. Or you can manage your Merchant account at Google Payment Centre -> Settings.
To add in-app purchase products go to the YOUR_APP > Store presence > In-app products menu. There are two type of in-app purchase products – Managed product and Subscription products. We will focus on the Managed Product. Click on Add new product button. Add the title and description of the product. Set a price for the product. When you are done, make sure you click on the Inactive button and activate this product.
Before you begin with API implementation, make sure that Android Native Vending API is enabled. See the screenshot below: