Staff Software Engineer, Fullstack

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 looking for a Fullstack Software Engineer who will be responsible for implementing the various backend systems that support all business features.

In this role, you will be part of the backend engineer team, responsible for the services and integrations that power our products, such as Payment, Billing, Identity, partner integration, etc. You'll be designing, developing, testing, and scaling systems needed to deliver great user and partner experiences.

You'll work closely with your product, design and engineering peers to solve our users' most pressing problems around rent payment. You'll roll out changes to our customers in an agile manner with a delivery cadence that favors small, frequent iterations. The ideal candidate will be comfortable leading scoping, design and implementation for APIs they build and can drive their production rollouts to completion with minimum oversight.

A minimum of 4 +years of experience with Java and 3+ with React/Typescript is required for this position.
What You'll Do

• Design, implement and maintain our Finance service and internal tooling, including financial reporting, reconciliation/audit process.
• Design and develop new APIs and functionalities to support large money movements across our banking partners via different payment rails, such ACH.
• Scale out core platform to support business growth while maintaining performance and reliability
• Continuously improving our daily operations with automation, tooling, design evolution, observability etc.
• Work closely with product, analytics, finance and engineering peers to launch new financial features into our platform

What We're Looking For:
Minimum Qualifications

• 6+ years of professional software development experience.
• 4+ years of hands-on experience with Java.
• 4+ years of experience with React or React Native.
• 4+ years of experience with TypeScript.
• Having experience building high-quality mobile and web UIs to specifications is a must to have.
• Experience leading the delivery of multiple highly impactful products end to end, on time with a high quality bar
• Ability to drive yourself and your team to bring quality and consistency to their code and architecture, without compromising velocity
• 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
• 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 architectures and tools in React Native and React ecosystems (Hooks, Components, Context, Redux).
• 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, to ensure high availability.
• 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 communicator, with experience in cross-functional collaboration.

The salary compensation range for this role will be commensurate with the candidate's experience and Flex's internal leveling guidelines and benchmarks.

• For working locations in NY/NJ/CA, the base salary pay range will be $221,000-$262,000
• For all other states, the base salary pay range will be $199,000-$236,000

Life at Flex:

We understand that it takes a diverse team of highly intelligent, curious, determined, empathetic, and self aware people to grow a successful company. Our HQ is located in New York City, but we have employees located throughout the US, Australia, Canada and South America. We are growing quickly, but deliberately, with a focus on building an inclusive culture. Our dynamic team has incredible perspectives to share, just as we know you do, and we take great pride in being an equal opportunity workplace.

We offer many employee benefits. For full time, U.S. based employees we offer:

• Competitive pay
• 100% company-paid medical, dental, and vision
• 401(k) + company equity
• Unlimited paid time off + 13 company paid holidays
• Parental leave
• Flex Cares Program
• Free Flex subscription

For full time non-US employees, we offer

• Competitive Pay
• Company Equity
• Unlimited PTO