Staff Software Engineer, Backend

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

Flex is hiring Staff Software Engineer, Backend roles across three engineering teams: Consumer, Partner Integrations, and Core Platform. When you apply, you will automatically be considered for all open Staff Backend positions, and your placement will be determined based on your experience and expertise assessed during the interview process.

As a Staff Engineer at Flex, you’ll help set technical direction and shape the long-term architecture of our backend services while still being hands-on with coding and delivery. You will collaborate across engineering, product, design, and other stakeholders to ensure scalable, reliable, and impactful systems that power consumer experiences, partner integrations, and our core business platforms.

You’ll also play a critical role in mentoring engineers, elevating technical standards, and ensuring the success of projects end-to-end.

Our Engineering Teams

• Consumer Engineering: Builds the APIs and backend systems powering Flex’s consumer-facing mobile and web apps. This team focuses on delivering scalable services for a seamless rent payment experience.

• Partner Integrations Engineering: Owns the backend services and integrations that connect Flex to financial partners and payment networks, ensuring secure, reliable payment flows and partner-facing experiences.

• Core Platform Engineering: Maintains the backend services and infrastructure supporting all business features, including Payments, Ledger, Identity, and Settlement, providing the foundation for all of Flex’s products.

What You’ll Do

• Design, build, and scale backend services and APIs that power Flex’s consumer apps, partner integrations, and core platforms.
• Provide technical leadership and guidance on system architecture, long-term vision, and team best practices.
• Lead the delivery of highly impactful products end-to-end, from requirements gathering to rollout, with high quality and timeliness.
• Work closely with product, design, and cross-functional teams to translate requirements into robust technical solutions.
• Build robust, fault-tolerant systems with multiple external dependencies in distributed environments.
• Drive adoption of best practices across the engineering org, including testing, observability, automation, and CI/CD.
• Mentor and support engineers on the team, raising the technical bar and fostering growth.
• Operate services in production with high availability, leveraging monitoring and observability tools.
• Contribute to evolving Flex’s service-oriented architecture, REST APIs, message queues, and scalable system design.
• Balance hands-on execution with architectural decision-making, ensuring velocity and long-term maintainability.

Who You Are

• 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.
• Experience leading the delivery of multiple high-impact projects end-to-end.
• 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 thr