How do you set a subscription application in MIT App Inventor?

How do I create a subscription application, is there a special setting in the application or directly through the Google Play Developer settings

Use an in app billing extension
You cam find extensions after doing a search here in the community ot the extensions directory


I really don't know the working mechanism of subscribing to applications. For me as a layman, of course this issue contains uncertainty rather than confidence.

Please enlighten me, on what side does the application work for this issue, and on the other hand there are setting rules in Google Developers.

Thank you in advance for your willingness to provide an explanation about this.