Senior Full-Stack Software Engineer

About the Role

We are looking for a Senior Full Stack Engineer to join the early team and help define how money moves on Fin. You will work closely with the CEO, CTO, and a small group of senior engineers to design and ship core product experiences, integrate with payment partners (Stripe, PayPal, on and off ramps, banks), and build the systems that let Fin handle millions of transactions safely and reliably.

This is a highly autonomous role where you own projects end to end, from shaping the spec to deployment, and see your work in the hands of real users quickly. If you care about building simple products on top of complex systems and are excited about fixing how global payments work, we would love to talk.

We value your time: our process focuses on practical system design and architectural discussions, not LeetCode grinding or unpaid take-home assignments.

What You Will Do

• Design, build, and ship full stack features across our web and mobile surfaces, from APIs and services to polished user interfaces.
• Own projects end to end: work with product and leadership to scope requirements, design systems, implement, test, and ship to production.
• Integrate third party payment and financial APIs, including processors, on and off ramps, compliance tooling, and identity providers.
• Build scalable, high performance services that handle real money movement with strong reliability and observability.
• Maintain a high bar for code quality through clean abstractions, tests, and thoughtful code review.
• Collaborate closely with product, design, and operations so that what we ship feels simple for users even when the underlying system is complex.

What You Need to Be Successful

• Deep experience with TypeScript and Node.js. We are mostly a TS shop with some pockets of Rust.
• Production experience with React Native. Bonus points if you are familiar with the Expo ecosystem and modern mobile build pipelines.
• Experience owning complex product changes from idea through launch, not just implementing narrow tickets.
• Deep comfort debugging across the stack, from database and infrastructure issues to front end performance problems.
• Solid understanding of security best practices, particularly around authentication, authorization, and handling sensitive data.
• A strong sense of code quality, including testing, readability, and maintainability in a fast moving environment.
• Clear written and verbal communication, and an ability to work closely with non engineering partners.
• High tolerance for ambiguity and the necessary shifting targets that exist in an early stage start up environment.

Bonus Points

• Experience in EITHER traditional fintech integrations (Stripe, Plaid, ACH rails) OR blockchain infrastructure (especially Solana in a production environment).
• Prior startup experience where you were an early engineer and had meaningful product ownership.