Flutter Android Chinese Payment Integration

I need a Flutter developer who can wire a Chinese payment gateway into my existing app on Android. I already have the gateway’s REST API, the official Android SDK, and sample integration code; your task is to connect these pieces so a user can complete a transaction inside the Flutter flow and receive the appropriate response from the gateway.

Here is what I expect from you:

• Add the native Android payment SDK to the Flutter project, exposing the necessary Dart methods through a platform channel (or an existing Flutter plugin if it matches the supplied SDK version).
• Invoke the payment flow from a given screen, pass my dynamic order parameters, and handle success, failure, and cancel callbacks.
• Parse the gateway’s JSON response, update the UI, and return control to Flutter without blocking the main thread.
• Provide brief inline comments plus a short README explaining any new dependencies, Gradle changes, or steps I must follow to build a release APK.
• Supply a demo APK or video showing a test transaction running on an Android device or emulator.

Everything should compile on the current stable Flutter channel. Once I can run the app, trigger a payment, and see the correct callback data printed in the console and reflected in the UI, the job is done.