Flutter App Razorpay Payment Integration

I have an Android application written in Flutter that is already live; the only missing piece is a robust payment flow. I need you to wire the app to Razorpay and support all three customer options—Cards, UPI, and Net banking—so users can pay in the way that suits them best.

Here is what must happen inside the app:
• Invoke the Razorpay checkout from my existing order screen and pass the correct amount and user details.
• Handle success, failure, or user-cancel callbacks gracefully and show clear messages on the UI.
• After a success callback, send the Razorpay payment ID to my backend and rely on Razorpay’s server-to-server payment-status webhooks to mark the order paid (no client-only confirmation).
• If the webhook reports a failure or refund, update the order status in the app accordingly.

Security is non-negotiable: all sensitive keys stay on the server, and client code uses only the publishable key. Please keep the code clean, well-commented, and 100 % null-safe. You may use the official razorpay_flutter package or a custom platform channel if a corner case demands it—but the end result must compile on the current Flutter stable channel and run smoothly on Android 8.0 and above.

Deliverables
1. Updated Flutter code (Dart + any required native snippets) committed to the repo via PR.
2. Sample Node/PHP snippet—or clear API contract—to receive Razorpay webhooks and verify the signature.
3. Step-by-step setup notes so I can reproduce the build and re-generate keys in the future.
4. A brief screen-recording (or GIF) showing a test payment from checkout through confirmed order status.

I’ll test with Razorpay’s test keys first, then move to live keys once everything passes. Looking forward to a seamless and secure integration.