Cross-Platform App Build Needed

I’m commissioning a complete Android and iOS application and need a developer who can take it from first sketch to App Store and Google Play submission. Core functionality • Registration must support email-and-password, social media login, and phone-number verification (OTP)... (Budget: $750 - $1500 USD, Jobs: Android, App Design, App Usability Analysis, Database Management, Flutter, iOS Development, Mobile App Development, Mobile App Testing, Mobile Development, Payment Gateway Integration)