I’m looking to have a native Android application built whose main purpose is to generate revenue directly through secure in-app payments. The flow is simple: users open the app, access premium content or services, and complete their purchase without leaving the Android environment. Because monetisation is the heart of this project, I need clean integration with Google Play Billing, a friction-free checkout experience, and reliable handling of payment confirmations and possible refunds. Beyond that core requirement, I’ll rely on your guidance for the most efficient architecture, recommended libraries, and any UI considerations that make paying feel fast and trustworthy. Please propose: • the tech stack you prefer for Android (Kotlin, Java, Jetpack Compose, etc.) • how you’ll secure transactions and user data • a brief outline of milestones from prototype to Play Store-ready release If you have live examples of previous Android apps that already process in-app payments, share a link or an APK so I can get a feel for your style and code quality.