iOS-Android Payment Integration Fixes

I have a fully-built mobile application that runs on both iOS and Android, but a few critical items still need attention before the next store release. First, I want seamless in-app payments: Apple Pay on iOS and Google Pay (or the standard Google in-app billing) on Android... (Budget: $30 - $250 USD, Jobs: Android, Android App Development, iOS Development, iPhone, Mobile App Development, Payment Gateway Integration, PHP, Xcode)