Step 1: Log into your Google Developer account here:
https://play.google.com/apps/publish/
Step 2: Click the Settings tab from the menu on the left.
Step 3: Scroll down to the bottom of this page and you’ll see a link to activate your Merchant account.
Note: When you have activated your Merchant account it will look like this.
Now that you’ve activated your Merchant account, you are required to obtain your License/Billing Key from your Google Developer account. Here’s how:
Step 1: From the menu on the left, select All Applications, then click on the app that you’re going to apply the in-app purchases to.
Step 2: From the menu on the left select Services and APIs found under Development Tools
Step 3: Copy the license key found in the section titled “Your license key for this application.”
Step 4: Upload your License/Billing Key to the Commerce section of your app’s control panel.
Note: Make sure you remove any spaces.
VERY IMPORTANT: Now that you have your Merchant account activated and your License/Billing Key uploaded, you will need to contact us. Before you can add the In-App Purchase products to your app in your Google Developer account, we must first upload a version of your app that has your License/Billing Key included.
Once this version has been uploaded, you are ready to start creating your In-App Purchase products, however, there are two different types that we currently support; Single (Managed Products) and Subscriptions. Depending on what type of product you are charging for, the steps may be slightly different. We’ve put together specific articles to walk you through them. Here’s how: