Wallet Backend & NFC Integration

I already have the complete Flutter front-end for my wallet app, Babypay.in. What I now need is the brains behind it: a rock-solid, PCI-DSS-compliant backend that can process transactions quickly and safely while letting users save multiple cards and pay with a single tap.

Core scope
• Transaction management is the heart of this build. Every peer-to-peer or merchant payment must move reliably through our system, log properly, and return clear success or failure responses.
• A secure multi-card vault is required so users can add, tokenise and manage several Indian debit/credit cards without ever exposing PAN data.
• NFC Tap & Pay must integrate seamlessly with the existing UI, triggering tokenised card pulls and passing credentials to the payment rails in real time.
• All code, storage and data flows must satisfy current PCI-DSS guidelines; I will need the accompanying compliance documentation.
• Because we operate in India, familiarity with domestic schemes (RuPay, Visa India rails, OTP flows, UPI collect for wallet top-ups, etc.) is essential.

Expected deliverables
1. Clean, well-documented backend code (language/framework of your choice) with REST/GraphQL endpoints aligned to the front-end screens.
2. Card vault microservice with token lifecycle management, BIN checks and fallback logic.
3. NFC Tap & Pay module wired into the existing Flutter code and demoed on a test build.
4. End-to-end transaction flows covering:
• Peer-to-peer transfers
• Merchant payments (static & dynamic QR or POS)
5. Deployment scripts, database schema and environment variables for staging and production.
6. PCI-DSS compliance checklist and logs proving encryption at rest and in transit.

Please bid only if you are based in India and have shipped at least one wallet, banking or payment gateway project that handled card tokenisation or NFC payments. Include a brief note on the Indian payment interfaces you have worked with and a link to a live app or repository I can review.