Senior 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 2026 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 Our Opportunities

Flex exists to make paying rent work the way real life actually works — smoothing out cash flow, helping renters avoid late fees, and letting them build credit instead of falling behind. As a Senior Backend Engineer, you'll design, build, and scale the services and integrations behind Payment, Billing, Identity, and partner integrations that keep rent moving on time for renters every month — leading scoping, design, and implementation for the APIs you own, driving your own production rollouts to completion with minimal oversight, and working closely with product, design, and engineering peers to solve renters' most pressing problems in small, frequent iterations rather than big, risky releases.
About Our Team(s)

We have some really exciting teams who are looking for an amazing engineer like you! Check them out!

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Partner Integrations - Partner integrations work to standardize APIs, tools, and processes that let external partners connect to Flex for data sharing and payments across entry points like Flex Anywhere and Quick-Pay

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Fin Platform - Fin Platform is the monitoring and operations layer for Flex 's billing and payment systems, covering dashboards, SLIs/SLOs, runbooks, deployment and on-call procedures to ensure reliability and readiness.

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Money Team - builds and owns the platforms, tooling, and documentation powering Flex 's payments, wallet, and settlement finance systems.

Who Thrives Here?

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A Doer — you get things done efficiently, and you're comfortable rolling up your sleeves when something's blocking the team.

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An Owner — you take full accountability for what you build, from design through production, and you always have a plan B.

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Someone Collaborative — you bring people together to pressure-test ideas rather than working in a silo.

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Someone with Precision — your code and your communication are both clear, because ideas only matter once others can act on them.

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Someone Resilient — systems break and priorities shift, and you adapt without losing momentum.

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Someone Humble — you care more about getting to the right answer than being the one who's 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 a high degree of ownership

- Experience working with technical and non-technical stakeholders, successfully aligning and setting expectations on scope and delivery

- Ability to grow in a fast-paced and dynamic environment that will challenge you to always bring your best

- Experience building robust, fault-tolerant systems with multiple external dependencies

- Experience designing, building, and maintaining data pipelines

- Proficient in Java frameworks and tools used at Flex , including 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