Android App: Auth & Purchases

I need a new Android-only application built from the ground up. The app must open with a clean user-authentication flow (email, social, or phone—whichever SDK you feel is fastest to integrate). Once signed in, users will see core content that can be expanded through in-app purchases... (Budget: ₹37500 - ₹75000 INR, Jobs: Android, Android App Development, Android Studio, Java, Kotlin, Mobile App Development, Mobile App Testing, Software Architecture)