Cross-Platform iOS & Android App Build

I need a mobile application that runs smoothly on both iOS and Android. The core idea is ready; what I now require is full development—from architecture and UI/UX through coding, testing, and store deployment... (Budget: ₹12500 - ₹37500 INR, Jobs: Android, Flutter, iOS Development, iPhone, Mobile App Development, React Native, Testing / QA, UI / User Interface)