: Backend Engineer — Payments Middleware & Fintech API Integration Budget: $60–$90/hr

$60–$90/hr | Part-time, 10–15 hrs/week | 4-month engagement About the Project We're a multichain dev collective building a non-custodial crypto payment product that lets users spend via Apple Pay and Google Wallet at Visa merchants globally, powered by a direct Visa integration, biometric auth, and on-chain DEX routing. Full details shared under NDA after a screening call. We need a backend engineer to own the middleware layer connecting it all. What You'll Build Middleware mapping JIT token swap logic to a card issuance API Biometric session management with a time-bound authorization window per user Multi-source CEX price feed integration: median calc, staleness detection, dropout handling Circuit breaker logic pausing authorizations on source dropout or price divergence Heartbeat reconciliation engine monitoring liquidity float and triggering replenishment Sandbox/testnet validation of the full payment flow You Are Strong with Node.js, Python, or Go Experienced integrating fintech/payments APIs (Stripe, Plaid, Marqeta, or similar) Comfortable with async settlement and real-time middleware Familiar with Web3 concepts (no contract dev needed, but understand on-chain swaps) Nice to Have Passkey/WebAuthn experience Prior work on crypto card, DeFi settlement, or reconciliation products