Senior Software Engineer, Backend

Socket.dev; New York (NY); Hybrid; USD 146,000 - 215,000; Full time

Benefits offered by this job

Company equity

Unlimited PTO

Parental leave

Free Flex subscription

Job summary

Flex, a NYC headquartered FinTech, is hiring a Senior Backend Engineer to design, build, and scale services for Payment, Billing, Identity and partner integrations. You’ll own API design and drive production rollouts with a cross-functional team.

Ideal candidates bring 6+ years in software engineering, strong Java experience, and proficiency with AWS, REST APIs and data pipelines. Hybrid roles in NYC with relocation options may apply.

Qualifications

• 6+ years of software engineering experience.
• 4+ years of Java experience.
• Experience working with globally distributed teams and ownership.
• Experience with REST APIs, data pipelines, and messaging.
• Experience with AWS and containerization tools.

Responsibilities

• Design, build and scale backend services for Payment, Billing, Identity and partner integrations.
• Lead scoping, design, and implementation for owned APIs with production rollout responsibility.
• Collaborate with product, design and engineering teams to deliver iterative improvements.

Skills

6+ years software engineering

Java

Distributed systems

REST APIs

AWS

CI/CD

Data pipelines

Software ownership

Spring framework

Containerization

Tools

Spring (core/web/boot)

Gradle

JUnit

JVM tuning

Job description

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!

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

Who Thrives Here?

• A Doer — you get things done efficiently, and you're comfortable rolling up your sleeves when something's blocking the team.
• An Owner — you take full accountability for what you build, from design through production, and you always have a plan B.
• Someone Collaborative — you bring people together to pressure-test ideas rather than working in a silo.
• Someone with Precision — your code and your communication are both clear, because ideas only matter once others can act on them.
• Someone Resilient — systems break and priorities shift, and you adapt without losing momentum.
• 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 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

Compensation

Flex takes a market-based approach to pay, and compensation may vary depending on your primary work location. Work locations are categorized into one of three tiers based on a cost of labor index for that geographic area. The successful candidate’s starting pay will be commensurate with their experience, qualifications, and Flex’s internal leveling guidelines and benchmarks.

• Tier 1 (NYC/Bay Area, Los Angeles, Seattle) $172,000 — $215,000 USD
• Tier 2 (Austin, Washington D.C. Philadelphia, San Diego, Chicago, Atlanta) $154,800 — $193,500 USD
• Tier 3 (Salt Lake City, all other USA cities) $146,200 — $182,750 USD

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.

Offices

Roles posted in New York, San Francisco, and Salt Lake City are hybrid positions with on-site expectations of 2-3 days per week in our local offices. For candidates outside of these areas, you may be eligible for our relocation assistance program.

Benefits

For full-time U.S. employees we offer:

• Competitive medical, dental, and vision
• Company equity
• 401(k) plan with company match
• Unlimited paid time off + 13 company paid holidays
• Parental leave
• Free Flex subscription

For full-time non-U.S. employees, we offer:

• Competitive compensation + company equity
• Unlimited PTO