How to enable In App Purchase facility at the time of Login?
Go to App Pages in the App Design section.
Click on System Pages and select Login feature.
In the Login area, you can switch on and off the Facebook login as per your needs.
Now go to Payment Settings to enable In App Purchase facility.
Here, you have Android Payment Credential section and iPhone Payment Credential section, where you need to provide a few details like Monthly Subscription Item ID, Yearly Subscription Item ID, One Time Subscription Product ID, and Public Key for Android credentials.
The tutorial present on the right side of the listing will guide you to activate in-app purchase in the Play Store.
Once you have activated the in-app purchase feature, click on Save & Finish to continue.