Mobile App API Integration

I have an existing mobile application that runs on both iOS and Android, and I now need a seamless integration with a third-party API. Your job is to wire the app to the new endpoints, handle authentication, parse the responses, and make sure everything is production-ready across the two platforms.

The core tasks include:
• Plugging the API into the existing codebase (both iOS and Android versions)
• Implementing secure token or key management in a way that satisfies App Store / Google Play guidelines
• Creating clean, reusable service classes or modules so future endpoints can be added easily
• Adding thorough error handling, retries, and graceful fallbacks for poor connectivity
• Writing concise in-code comments plus a short integration guide so my team can maintain it later
• Testing the finished build on real devices for each platform and confirming the calls succeed end-to-end

When you hand the project back, I expect the updated source code, a brief changelog, and a quick demo clip or TestFlight/Internal-Test APK that shows the integration working. If you have experience with Swift, Kotlin, or a cross-platform stack such as React Native or Flutter, please mention it when you respond.