finalising in-app subscription payment for Nativescript Vue App

built a app using Nativescript Vue - the app is working well in Testflight and we have submitted it to Apple for approval to go-live in the app store - however there are a few quirks with the in-app purchase plugin that has been used. There is inconsistent behaviour occurring in testing - mostly works as expected however other times there are unusual user journeys being triggered (multiple purchases etc).