Staff Software Engineer, Backend, Money Team

We are seeking a Staff Software Engineer to join our Money Team, responsible for building and scaling the financial infrastructure that powers payments, billing, subscriptions, payouts, ledgers, and other money movement systems across the company.

As a Staff Engineer, you will provide technical leadership across multiple teams, drive the architecture of mission-critical financial platforms, and help ensure our systems are secure, reliable, compliant, and scalable. You will partner closely with Product, Finance, Risk, Compliance, Data, and Engineering teams to deliver high-impact solutions that directly affect revenue, customer experience, and business operations.

What You'll Do

• Design, build, and scale backend services and APIs that power Flex's core financial infrastructure, including payments, money movement, billing, settlements, reconciliation, and ledger systems.
• Lead the architecture and evolution of highly available, fault-tolerant financial platforms that process and track millions of dollars in transactions with accuracy, reliability, and auditability.
• Provide technical leadership and guidance on distributed systems design, financial data consistency, transaction integrity, and long-term platform strategy.
• Drive the delivery of highly impactful initiatives end-to-end, from requirements gathering and technical design through implementation, rollout, and operational excellence.
• Partner closely with Product, Finance, Risk, Compliance, Operations, and cross-functional engineering teams to deliver scalable and compliant payment experiences.
• Build robust systems that integrate with external payment processors, banking partners, card networks, and financial service providers.
• Design and implement resilient ledger, settlement, and reconciliation workflows that ensure financial accuracy across the ecosystem.
• Drive adoption of engineering best practices across the organization, including observability, automated testing, reliability engineering, CI/CD, and secure software development.
• Mentor and support engineers on the team, raising the technical bar and fostering a culture of technical excellence and ownership.
• Operate mission-critical financial services in production with stringent uptime, security, compliance, and performance requirements.
• Contribute to the evolution of Flex's service-oriented architecture, event-driven systems, APIs, message queues, and scalable financial platforms.
• Balance hands-on execution with architectural leadership, ensuring both rapid delivery and long-term maintainability of critical money movement systems.

• 6-8+ years of professional software engineering experience, with a focus on backend development.
• 4+ years of hands-on Java experience (Spring core/web/boot, Gradle, JUnit, JVM tuning & performance).
• Strong computer science fundamentals and proven experience designing scalable, distributed systems.
• Deep experience building or operating financial systems, including payments, money movement, ledgers, settlements, reconciliation, billing, or banking infrastructure.
• Experience integrating with payment processors, settlement, card networks, banking partners.
• Strong understanding of transactional systems, financial data consistency, idempotency, auditability, and fault tolerance in distributed environments.
• Skilled at working with both technical and non-technical stakeholders, aligning on scope and delivery.
• Ability to write high-quality, testable, maintainable, and secure code.
• Hands-on experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB), containerization (Docker/Kubernetes), and relational + NoSQL databases (MySQL, PostgreSQL, DynamoDB).
• Proficient with CI/CD pipelines (GitHub Actions preferred), git, and build automation.
• Familiar with observability and monitoring tools (e.g., DataDog) for maintaining service availability.
• Excellent communicator, comfortable collaborating in globally distributed teams.
• Track record of mentoring engineers and raising team standards through best practices.

Life at Flex

We understand that it takes a diverse team of highly intelligent, curious, determined, empathetic, and self aware people to grow a successful company. Our HQ is located in New York City, but we have employees located throughout the US, Australia, Canada and South America. We are growing quickly, but deliberately, with a focus on building an inclusive culture. Our dynamic team has incredible perspectives to share, just as we know you do, and we take great pride in being an equal opportunity workplace.

3.63.6 out of 5 stars San Francisco, CA Remote $200,000 - $250,000 a year - Full-time, Pulled from the full job description

• Parental leave
• Health insurance
• 401(k) matching
• Vision insurance
• Dental insurance
• Relocation assistance
• Unlimited paid time off, For full-time U.S. employees we offer:
• Competitive medical, dental, and vision
• Company equity
• 401(k) plan with company match
• Unlimited paid time off + 13 company paid holidays
• Parental leave
• Free Flex subscription

For full-time non-U.S. employees, we offer:

• Competitive compensation + company equity
• Unlimited PTO

Flex is a growth-stage, NYC headquartered FinTech company that is creating the best rent payment experience. It's hard to believe that it's 2026 and paying rent on time is expensive, inflexible, and difficult. We're here to change that! Flex enables our users to pay rent throughout the month on a schedule that better fits their finances and budget. Our mission is to empower as many renters as possible with flexibility over their most significant recurring expense. After deliberately keeping a stealth profile as we built up unprecedented investor support and an enthusiastic user base, we are looking for motivated individuals to help us keep our mission growing. Will you be a part of the team?