if you want to publish your app in Google Play, then you should read this
and use Google In App Billing, see also my billing extension here 404 Not Found | Pura Vida Apps
September 28, 2020:
We’re updating our Payments policy to clarify when Google Play’s billing system should be used for in-app purchases. This clarification is important to increase user protections across Play-distributed apps and makes the policy easier to understand.
Any existing app that is currently using an alternative billing system will need to remove it to comply with this update. For those apps, we are offering an extended grace period until September 30, 2021 to make any required changes. New apps submitted after January 20, 2021 will need to be in compliance.
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.