Description: We are looking for an experienced Web3/payment engineer to integrate a crypto payment checkout gateway into our existing marketplace platform. Our stack is React frontend + Node/Express backend (marketplace architecture). We need someone who can deliver a secure, clean, and production-ready integration with clear documentation. Scope of Work: * Integrate a crypto payment provider into checkout flow * Build backend payment endpoints + webhook handlers * Verify payments and update order/transaction state * Handle edge cases (expired payments, under/overpayment, failed confirmations, duplicate webhooks) * Implement secure secrets/config management * Add logs and basic monitoring for payment events * Provide technical documentation + handover Required Experience: * Proven crypto payment integrations (Coinbase Commerce / BitPay / NOWPayments / Stripe crypto / similar) * Strong Node.js/Express + React experience * Solid webhook security and idempotency knowledge * Production payment reliability mindset Nice to Have: * Marketplace/e-commerce checkout experience * Stablecoin and multi-chain knowledge * Experience with Sharetribe-style platforms Deliverables: 1. End-to-end crypto checkout integrated 2. Webhook verification + transaction sync 3. Admin-visible payment status mapping 4. Deployment/config guide 5. Test checklist + post-launch support window To Apply, Please Include: * 2-3 relevant projects with links * Which payment provider you recommend and why * Estimated timeline (MVP + production hardening) * Your approach to webhook reliability and security * Your timezone and weekly availability Engagement: * Remote, flexible * Start: ASAP * Potential for long-term work