Software Engineer II, Backend

About Flex

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 Job

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

As a Backend Engineer at Flex, you will be responsible for designing, building, testing, and scaling backend services and APIs that power our consumer products, partner integrations, and core business systems. You’ll work closely with product, design, and engineering peers to solve renters’ most pressing problems and deliver delightful user and partner experiences.

You will own the full lifecycle of your services- from scoping and architecture to deployment and monitoring, and will roll out changes in an agile, iterative manner to deliver impact quickly.

Our Engineering Teams

• Consumer Engineering: Builds the APIs and backend systems that power Flex’s main consumer-facing products. This team focuses on delivering scalable services that drive a seamless rent payment experience through our mobile and web apps.
• Partner Engineering: Focuses on our partner integrations platform and partner-facing experiences. This team owns the backend services and external integrations that connect Flex to financial and other third-party partners to ensure reliable, secure rent payment flows.
• Core Platform Engineering: Builds and maintains the backend systems and infrastructure that support all business features, including Payments, Billing, Identity, and Partner Integrations. This team ensures Flex’s foundation is robust, scalable, and secure.

What You'll Do

• Design, develop, test, and scale backend services and APIs that power Flex’s products, partner experiences, and internal platforms.
• Implement the service APIs used by our mobile and web apps to simplify complex rent payment processing.
• Build robust, fault-tolerant systems that integrate with multiple external dependencies and ensure high reliability.
• Work closely with cross-functional teams—including Engineering, Product, Design, Infrastructure, Sales, Partner, and Customer Success—to deliver features and integrations that wow both customers and partners.
• Translate feature requirements into well-structured technical specifications and scalable solutions.
• Lead scoping, design, and implementation for the APIs you build and drive production rollouts with minimal oversight.
• Contribute to service-oriented architecture, scalable system design, and internal best practices for distributed services environments.
• Collaborate with peers to evolve Flex’s technical architecture as the company and product offerings grow.
• Ensure services are observable and highly available through effective use of monitoring tools and practices.
• Participate in code reviews, CI/CD improvements, and efforts to increase code quality and stability.

Key Qualifications

• Strong computer science fundamentals and passion for building scalable backend systems.
• 2–3+ years of professional software engineering experience with a focus on backend services.
• Proficient in Java with hands-on experience using Flex’s core stack: Spring (core/web/boot), Gradle, JUnit.
• Experience building and ma