Senior Software Engineer, Stablecoin Payments

Flex is building AI-native financial services for business owners.   We’re re-architecting the entire financial system for entrepreneurs—from the first dollar a business earns to how that value compounds, moves, and is ultimately spent in real life. Banking, credit, payments, personal finance, and financial operations—rebuilt from the ground up as a single, intelligent system. Flex is the full financial home for ambitious owners.   Since launching publicly in September 2023, Flex has scaled from zero to nine-figure annualized revenue, with a clear path to profitability by late 2026. We move fast, ship relentlessly, and operate with extreme ownership.   Our customers are affluent business owners ($3–$200M in revenue)—the backbone of the economy and one of the most underserved segments in finance. They’re stuck with outdated banks and fragmented tools. We’re replacing all of it. The opportunity is massive: a ~$1T+ revenue market hiding in plain sight. Our ambition is to build a $100B+ company by delivering a product that is fundamentally better—not incrementally improved.   Flex has raised $100M+ in equity and $300M+ in debt.   - Mission-critical problems: We build software that directly controls how money moves at scale. - High bar, low ego: Small teams, exceptional people, real ownership. - Speed over comfort: We prioritize execution, quality, clarity, and results. - Enduring impact: What we’re building will define how a generation of owners runs their businesses.   Team & Locations   We hire exceptional people who want to build hard things and see their work matter immediately. Roles are available in: San Francisco, Miami, New York, and fully remote.   Flex Fuels Ambition.

About the Role

Flex is building stablecoin products for business owners, and we need engineers who can ship them. The team is small and moving fast, and you’ll be one of the first engineers to join. You’ll build the services that move customer money on-chain and connect them to the banking systems Flex already runs. That means real ownership, direct access to the engineering lead and product, and work that customers use.

Crypto experience helps, but it isn’t required. Much of the work is strong fintech engineering: payments, onboarding, compliance, and reliability. If you’ve built that kind of system and want to learn the crypto side, we want to talk.

What You'll Do

• Design, build, and run backend services for stablecoin payments, including deposits, withdrawals, and on and off ramps
• Integrate with partners for wallets, virtual accounts, and stablecoin orchestration
• Build business onboarding (KYB) and compliance flows that stand up to banking audits
• Connect new stablecoin products to Flex’s existing banking, ledger, and payments systems
• Own your work from design through launch and production support
• Work closely with product, design, compliance, and business development
• Help set technical direction of the team’s roadmap 
• Onboard and mentor new teammates 

Requirements

• 5+ years of backend software engineering experience
• Experience building and running production services in fintech, payments, or banking
• Experience with compliance-driven systems such as KYB, KYC, AML, or audit requirements, and comfort working with compliance stakeholders
• Strong system design skills, especially for money movement: accuracy, reliability, and handling failures safely
• Proficiency in a modern backend language 
• Comfortable owning problems end to end in a small, fast-moving team
• Clear communicator with technical and non-technical partners

Nice to Haves

• Hands-on crypto experience: stablecoins, wallets, custody, on-chain transactions, etc.
• Experience with on and off ramps, virtual accounts, or stablecoin orchestration
• Smart contract development or auditing experience
• Prior experience at a startup or high-growth company

Why Join Us   Build something generational — Capture the full lifecycle of money for ambitious business owners. Work on real money, real risk — Payments, credit, and banking at serious scale. Solve hard problems — AI, underwriting, compliance, and global finance from first principles. True ownership — Small teams, high trust, real accountability. Founder-level exposure — Direct access to leadership, customers, and investors. High bar, high taste — Move fast without cutting corners. Elite peers — People here are builders, not tourists. Real upside — Meaningful equity if you help build something big.