Senior Backend Engineer

Flex is a growth-stage, NYC headquartered FinTech company dedicated to revolutionizing rent payment experiences. In 2026, paying rent on time remains expensive, inflexible, and challenging. Flex aims to change this by enabling users to pay rent throughout the month on a schedule that aligns with their finances and budget. Their mission is to empower renters with flexibility over their most significant recurring expense.

As a Senior Backend Engineer, you will design, build, and scale the services and integrations behind Payment, Billing, Identity, and partner integrations. This ensures rent moves smoothly and on time for renters every month. Your responsibilities include:

• Leading scoping, design, and implementation for the APIs you own
• Driving production rollouts to completion with minimal oversight
• Collaborating closely with product, design, and engineering peers to solve renters' most pressing problems in small, frequent iterations

Flex operates across several key teams:

• Partner Integrations - Standardizes APIs, tools, and processes for data sharing and payments across platforms like Flex Anywhere and Quick-Pay
• Fin Platform - Monitors and operates Flex’s billing and payment systems, covering dashboards, SLIs/SLOs, runbooks, deployment, and on-call procedures to ensure reliability and readiness
• Money Team - Builds and owns platforms, tooling, and documentation for Flex’s payments, wallet, and settlement finance systems

Who thrives at Flex?

• A Doer – You get things done efficiently and are comfortable rolling up your sleeves when obstacles arise
• An Owner – You take full accountability for what you build, from design through production, and always have a plan B
• Someone Collaborative – You bring people together to pressure-test ideas rather than working in isolation
• Someone with Precision – Your code and communication are clear, ensuring ideas are actionable
• Someone Resilient – You adapt to system failures and shifting priorities without losing momentum
• Someone Humble – You prioritize finding the right answer over being right

Qualifications:

Minimum Qualifications:

• Minimum of 6 years experience in software engineering
• Minimum of 4 years experience with Java
• Ability to work on a globally-distributed team with high ownership
• Experience working with technical and non-technical stakeholders, aligning on scope and delivery
• Ability to thrive in a fast-paced, dynamic environment
• Experience building robust, fault-tolerant systems with multiple external dependencies
• Experience designing, building, and maintaining data pipelines
• Proficient in Java frameworks and tools: Spring (core/web/boot), Gradle, JUnit, and JVM (memory/performance tuning, GC)
• Experience with Service-Oriented Architecture, REST APIs, Message Queues, and scalable architectures
• Experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB) and containerization tools

Preferred Qualifications:

• Proficient in CI/CD systems (preferably GitHub Actions), git, and automation
• Skilled in observability and monitoring tools, such as DataDog
• Experienced with big data platforms and tooling, including Snowflake
• Proficient in Infrastructure as Code, using tools like CDK and Terraform
• Skilled at elevating team standards through best practices and mentoring junior engineers
• Excellent written and verbal communication, with experience in cross-functional collaboration