Senior Fullstack Engineer, Payments

Alt is unlocking the value of alternative assets, starting with the $5 B trading-card market. We let collectors buy, sell, vault, and finance their cards in one place and we are backed by leaders at Stripe, Coinbase, Seven Seven Six, and pro athletes like Tom Brady and Giannis Antetokounmpo. Our next frontier is real-time pricing at scale—the Alt Value that powers every trade, loan, and product on the platform. We’re looking for a Senior Fullstack Engineer who wants to build the financial engine of our platform. You’re not just building a checkout flow; you’re powering the liquidity that makes this marketplace work. You’ll join a high-impact team responsible for our custom double-entry ledger, payment provider integrations, and our core lending products. If you have a "measure twice, cut once" mindset for backend integrity but still move with a bias toward action on the frontend, you’ll thrive here. What You’ll Do Here: Engineer Financial Integrity: Build and maintain our custom-built double-entry ledger system to ensure every cent is accounted for across the platform. Own Lending Infrastructure: Design and scale our lending products—from the logic of credit disbursements to the automated lifecycle of loan management. Architect Integrations: Design and implement robust integrations with payment gateways and banking partners, ensuring 99.99% reliability and seamless reconciliation. Own the UX of Money: Create high-trust user interfaces for payments and lending that make complex financial actions feel simple, transparent, and secure. Balance Rigor with Speed: Make thoughtful trade-offs between rapid feature shipping and the uncompromising correctness required for financial systems. Be a Multiplier: Level up the team through rigorous code reviews, technical documentation, and mentorship. This is a perfect fit if you… Are Obsessed with Correctness: You understand that in payments, "mostly working" is a failure. You think deeply about idempotency, race conditions, and da