Integrate Codes for Multiplatform Mobile App

I need a competent developer skilled in both Android and iOS development, or adept at React Native development. The task involves integrating two different codes into a mobile application for both Android and iOS platforms. The features to be integrated include:

* User Authentication
* Content Management
* In-app purchases
* Database
* UI/UX
* Cross Platform Application Development
* Implementing Navigation

The applicants should have proficiency in Java, Swift, and JavaScript language. If you are a seasoned developer with the ability to work across different programming languages efficiently, even better. This project requires a deep understanding of cross-platform application development and excellent problem-solving abilities. I look forward to working with a diligent and result-oriented professional.