Senior Backend + Mobile Engineer — Payment Card Integration (Solana/USDC)

Senior Backend + Mobile Engineer — Payment Card Integration (Solana/USDC) We're building a Web3 super app on Solana with a self-custody USDC wallet, payment cards, encrypted messenger, and social platform. We're preparing for a global launch in late August and need an experienced engineer to own the card integration layer across multiple providers and geographies. What you'll build: Backend (Python/FastAPI): — Multi-provider card issuer abstraction layer: standardized adapter interface so adding a new card issuer requires writing one adapter file with zero changes to wallet, settlement, or mobile code — Cardholder onboarding flow: KYC handoff to issuer, card creation, activation, freeze/cancel lifecycle — On-chain funding pipeline: Solana USDC to cross-chain bridge (Solana to EVM) to merchant deposit, fully automated with self-healing retry — Webhook receiver: signature-verified, deduplicated, dispatching all card event categories (authorization, settlement, refund, chargeback, 3DS challenge) — Auto top-up engine: confirmed on-chain deposit triggers automatic card funding, no manual steps — 3DS/OTP handling: decrypt incoming 3DS challenge, deliver OTP to user via in-app modal, handle response flow — Event ledger: full audit trail of every card action with lifecycle state tracking (pending, bridged, funded, settled) — Funding state machine with DB-backed lifecycle tracking Mobile (React Native): — Card UI screens: virtual card display, card-detail reveal (secure), balance view — 3DS OTP in-app modal with copy button (not push notification) — On-chain transaction signing via device wallet — Integration with existing self-custody wallet infrastructure Tech stack: — Python / FastAPI (backend API) — Solana / Anchor (smart contracts, on-chain signing) — Cross-chain bridging (Solana to BSC/EVM) — React Native (iOS + Android) — PostgreSQL, Redis, Kafka — Webhook signature verification, idempotent event processing Must-have experience: — Production card integration with at least one card issuer (prepaid, debit, or virtual) — Solana or EVM smart contract interaction from backend — Cross-chain bridge integration (any bridge protocol) — Webhook-driven event architectures with idempotency — 3DS / OTP / SCA payment authentication flows — React Native with native module experience — Clean, tested code: we expect 60%+ unit test coverage on financial flows Nice to have: — USDC / stablecoin payment experience — Multi-provider abstraction patterns (provider-agnostic interfaces) — Experience with card networks (Visa/Mastercard authorization, settlement, chargebacks) — SOC 2 compliant development practices Working model: — Milestone-based contract — You'll work alongside our lead dev who handles code review and deployments — PR review turnaround: 1 business day from our side — Direct communication with the founder — Timezone flexibility, async-first with availability for quick sync calls when needed To apply, include: — A brief description of a card integration you've built (issuer, scale, your role) — One example of cross-chain or blockchain payment work — Your availability and earliest start date — Hourly rate or fixed-price preference We move fast. If you're the right fit, we'll have you onboarded within 48 hours.