Senior Software Engineer, Backend Money Team

About the job

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 2025 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?

About The Role
We are seeking a Senior 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 Senior 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.
• 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 payment, ledger, settlement, and reconciliation workflows that ensure financial accuracy across the ecosystem.
• 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.

Who You Are

• 5+ years of professional software engineering experience, with a focus on Java backend development(Spring core/web/boot, Gradle, JUnit, JVM tuning & performance).
• Strong computer science fundamentals and proven experience designing scalable, distributed systems.
• 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.