Senior Software Engineer, Backend

Flex is a growth-stage FinTech company based in NYC, focused on revolutionizing the rent payment experience. They are seeking a Senior Backend Engineer to design, build, and scale backend services and APIs, collaborating with cross-functional teams to deliver robust systems that enhance the user experience.

Responsibilities:

• Design, develop, test, and scale backend services and APIs that power Flex’s consumer products, partner integrations, risk management systems, and core platform services
• Build and operate robust, fault-tolerant distributed systems with multiple external dependencies
• Implement service APIs for web and mobile apps, simplifying complex rent payment processing
• Work closely with Product, Design, Infrastructure, Sales, Partner, and Customer Success to deliver features and integrations that delight customers and partners
• Translate feature requirements into technical specifications and lead the architecture and implementation of scalable solutions
• Drive the full lifecycle of services and APIs you build, including deployment, monitoring, and optimization for high availability and performance
• Contribute to evolving Flex’s service-oriented architecture, REST APIs, message queues, and scalable systems design
• Develop risk management systems such as rules engines, ML-powered fraud detection, and high-scale event ingestion pipelines
• Mentor junior engineers and help elevate the team’s engineering practices through code reviews, architecture discussions, and technical leadership
• Ensure services are observable and reliable using monitoring tools and industry best practices
• Collaborate on CI/CD improvements and automation to increase code quality and delivery velocity

Requirements:

• A minimum of 4 years of experience with Java is required for this position
• Strong computer science fundamentals with a proven track record of building scalable backend systems
• 5–6+ years of professional software engineering experience with a focus on backend development
• 4+ years of hands-on Java experience, with deep knowledge of the Java ecosystem
• Proficient in Java frameworks and tools used at Flex: Spring (core/web/boot), Gradle, JUnit, JVM tuning and performance optimization
• Experience operating services in distributed, service-oriented architectures at scale
• Familiarity with REST API design, mobile API best practices, and message-driven architectures
• Skilled at building robust, fault-tolerant systems and integrating with multiple external dependencies
• Experience designing and maintaining data pipelines and working with big data platforms (bonus: Snowflake)
• Hands-on experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB), containerization (Docker/Kubernetes), and Infrastructure as Code (CDK/Terraform)
• Skilled in observability and monitoring tools (e.g., DataDog) to ensure high availability
• Ability to write high-quality code that is testable, maintainable, scalable, and secure, using industry best practices throughout the SDLC (unit testing, build automation, CI/CD)
• Excellent communicator, comfortable working with distributed teams and cross-functional stakeholders
• Proven ability to mentor junior engineers and raise the technical bar through best practices
• Experience in risk engineering, rules engine architecture, and implementing risk/fraud/credit policies in production systems is highly valued