An Ionic 5 app I built for a client uses Paypal for subscription, and Google rejected it because it doesn't use Google Play's billing system. Does it mean that Paypal is no longer accepted as a payment option on Android apps? The client really wants to use Paypal.
This is what Google says about InApp billing. Blog
Starting August 2, 2021, all new apps must use Billing Library version 3 or newer. By November 1, 2021, all updates to existing apps must use Billing Library version 3 or newer.
If you are distributing your app through the google play store, you must use Google Play Billing Library. It does not depend upon the framework you use. It applies to Native development, Ionic, Flutter, React Native, Xamarin etc. No other payment methods like Stripe, Paypal etc are accepted. The main problem here is that Google will take 30% of the total amount say it for one time or subscription. If you are keen on integrating Paypal you must distribute your app through ApkMonk, F-droid etc, or make payment options available only through your web app like Spotify, Netflix etc.