Senior TypeScript / Next.js Engineer for Payments Integration & Go-Live (Existing Codebase)

Overview I'm looking for a senior developer to help take an existing payments web app to launch. The codebase is TypeScript / Next.js (App Router) / Node.js / Prisma / PostgreSQL, built to a high standard with AI-assisted development (Claude Code): strict typing, CI that blocks on failures, tests on the money logic, and payments behind clean provider interfaces. The build is well underway. What I need is someone to audit it, validate the live payment integrations, harden it, and take it live. What you'll do Start with a short, paid code audit of the repo against its spec. This is the first task, and how we get to know each other's working style. Wire up and validate the live payment integrations (card acquiring and payouts) from sandbox through to production. Harden the money path: webhooks, idempotency, reconciliation, and the double-entry ledger. Take the app to go-live and support the early post-launch period. Must-haves Strong in TypeScript, Next.js (App Router), Node.js, Prisma, PostgreSQL. Demonstrable payment-integration experience: card acquiring, payouts, or marketplace/Connect-style work, including tokenisation, webhooks, idempotency, KYC, and ledgers. Comfortable working inside an existing codebase and with AI-assisted development (Claude Code, Cursor, Copilot). This is a hard requirement, not a nice-to-have. Available now and able to commit substantial hours. Stripe Connect or similar marketplace/payments experience is ideal. You'll be integrating specialist gateways and a payout provider, so what matters is transferable payments skill and comfort working across providers, not experience with one specific one. How we work Small, reviewed pull requests, one at a time. Strict typing and tests on anything that touches money. Payments sit behind provider interfaces with mocks, so you're validating and wiring real adapters, not rebuilding the app. Clear written communication and reliable async updates matter. To apply, please tell me: Your relevant payments work (what, and with which providers). Examples of working inside existing codebases and with AI coding tools. Your availability: can you start now, and how many hours a week. A portfolio and, if you have them, a couple of references. Some product details will be shared under a short NDA after an initial conversation. The engagement begins with the small paid audit before any larger commitment.