Flutter PhonePe Payment Integration

I have a Flutter mobile app that is ready for production, but I still need to wire in PhonePe V2 for live payments. My immediate goal is straightforward: allow users to complete purchases inside the app through PhonePe’s secure gateway. The flow must support both UPI and Credit/Debit Card options that PhonePe exposes, fall back gracefully if either fails, and return clear success or failure callbacks to my Dart code.

The UI is already built; what I need is the full back-end and client-side integration—generating the checksum on my server, initiating the transaction from Flutter, handling redirects or deep-links, verifying the response, and recording the final status locally. Please keep the implementation modular so I can update to future SDK versions without a rewrite.

Deliverables
• Complete Flutter code (Dart) that initiates a PhonePe V2 payment, handles UPI and Card flows, and parses the final transaction response.
• A lightweight Node (or comparable) example for checksum generation and verification.
• Clear setup notes so another dev can replicate the integration and run a quick sandbox test.

Acceptance criteria: I can build the app, run it on Android, choose either UPI or Card, complete a ₹1 test payment in the PhonePe sandbox, and receive a verified “SUCCESS” status back in Flutter without crashes or silent failures.

Backend: Laravel

I need immediately. Need to work remotely.