calling a trusted third party payment tool in a web view inside an ionic app.

Hey,
Well, I do not if you know it, but google just sent in the last developer policy they will not allow any third-party payment system in apps going to their apps store from Jan 20, 2021, so I am just guessing you are developing for android as well since you are using ionic, you will have to use the google store payment system, so I am guessing apple payment is the same (I can't give you a firm answer apple since I am still learning their policies).

Google: "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."