Fitness Mobile Application

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I am looking for a full-stack developer to create a fitness mobile application MVP that will be available on both iOS and Android platforms. The ideal candidate should have experience in developing cross-platform apps with React Native and for Back-End Java or .net.

Features to be included in the app are a workout tracker, diet planner, and a few other features, I would like the app to have a video conference feature and a personal gym assistant (This feature is outsourced).

Important: Messaging and Video conference is outsourced to an online company.
Development rules:

General
1- Deliver the back-end first, followed by Android and iOS
2- Multiple languages: English (LTR) and Farsi (RTL).
3- Daily (or every other day) code pushes to our Git repository
4- Provide a guarantee for 3 months after the work is completed (for bug fixes)

Technical:
1- APIs should have a successful, failed, and message pattern
2- Implement Google Crashlytics
3- Android version 7 is required
4- All API calls require OAuth2 authentication
5- The application class should contain all the configuration for the app
6- An app should be built on a library base, for example, Language Helper is a library the App uses, or Video Conference should be separate from the App.