Android/iOS App Development -- 2

I need a complete, ready-to-use mobile application that runs smoothly on both Android and iPhone. The core goal is to move from concept to a fully functioning app I can publish in Google Play and the App Store, not just a prototype... (Budget: $5000 - $10000 USD, Jobs: Android, Flutter, iOS, iPhone, Mobile App Development, React Native, REST API, Testing / QA)