Service Request Management App

I need a cross-platform mobile app for iOS and Android that pulls in live service-request calls and gives my field employees everything they need to handle those jobs from their phones and if possible the service requests are linked from the call center where the actual requests are registered... (Budget: $250 - $750 USD, Jobs: Android, API Integration, Backend Development, Database Management, Flutter, iOS Development, iPhone, Mobile App Development, PHP, React Native)