Flex is a growth-stage, NYC headquartered FinTech company that is building the payment layer for life’s financial obligations, giving households one place to see, split, and pay their bills around how they live and get paid. By offering greater choice over how and when payments are made and allowing eligible on time payments to help build a positive credit history, Flex puts households back in control of their cash flow.

That work brings together people with different perspectives who challenge the status quo and take ownership of solving difficult problems. For you, that means doing the best work of your career next to people who make you better, and together bringing ideas to life that make a real impact for the people we serve.

About the role

Flex is looking for a Staff Software Engineer to build and scale our Fraud and Payment Risk Platform. You will lead the architecture and hands-on development of backend services and shared infrastructure for fraud prevention and payment risk decisioning.

The platform combines real-time, near-real-time, and offline/batch-computed risk features with business rules, machine learning model outputs, and experimentation. You will make these capabilities reliable, scalable, and observable, enabling teams to develop, validate, and launch risk strategies faster and more safely.

This is a hands-on backend and platform role with technical ownership from architecture through production. You will collaborate with product, risk policy, data science, and engineering teams to turn risk strategies into reusable platform capabilities. Your scope includes feature ingestion and integration, user acceptance testing (UAT), experimentation, and engineering infrastructure supporting the full machine learning (ML) lifecycle—from development and validation workflows through deployment, serving, and production monitoring—in partnership with data scientists who own model research and training.

What you’ll do

• Lead backend architecture and development for the Fraud and Payment Risk Platform, including decisioning services, APIs, and shared infrastructure for evolving business needs.
• Design for scalability, performance, and reliability, balancing latency, throughput, availability, data consistency, and cost.
• Build capabilities for feature ingestion, integration, and serving, supporting real-time, near-real-time, and offline/batch-computed features with attention to freshness, correctness, and availability.
• Develop infrastructure for rules and experimentation, enabling teams to configure and version risk strategies, perform user acceptance testing (UAT), evaluate changes, and safely roll them out.
• Own engineering infrastructure across the ML lifecycle, supporting development and validation workflows, deployment, inference, versioning, safe rollouts, rollback, and integration of model outputs into risk decisions.
• Own monitoring and alerting across the platform, covering service health, feature freshness and quality, rule and experiment execution, and model inference. Partner with risk policy and data science teams to monitor model behavior and decision outcomes.
• Improve platform extensibility and usability, so teams can add features, rules, models, and experiments without duplicating infrastructure or tightly coupling systems.
• Drive complex initiatives from design through production, including technical design proposals, hands-on implementation, performance testing, migration planning, and cross-team coordination.
• Raise the engineering bar through design and code reviews, mentorship, and improvements to testing, documentation, deployment safety, and operations.

Our backend stack includes Java, Spring Boot, Python, and AWS.

Qualifications

Minimum qualifications

• 6+ years of professional software engineering experience, including substantial experience building and operating backend systems in production.
• 5+ years of hands-on Java experience, including building services with Spring Boot.
• Experience leading the architecture and delivery of complex distributed systems or shared backend platforms.
• Strong understanding of API design, service integration, data modeling, caching, and distributed-system failure modes.
• Experience diagnosing performance bottlenecks and improving scalability and reliability through measurement, testing, and production troubleshooting.
• Experience with cloud infrastructure, containerized deployments, and relational and NoSQL data stores.
• Experience establishing observability, monitoring, and alerting for production systems.
• Ability to lead technical decisions across teams, communicate architectural trade-offs clearly, and mentor other engineers.

Preferred qualifications

• Experience building risk platforms, decision engines, or fraud/payment risk systems is a plus, though risk-domain experience is not required
• Experience with feature platforms, configurable rules engines, experimentation infrastructure, or production model-serving systems.
• Experience building shared platforms that other engineering or risk teams adopt and operate independently.
• Familiarity with AWS services such as EKS, Aurora, ElastiCache, and DynamoDB.
• Experience with infrastructure as code and CI/CD automation using tools such as Terraform, CDK, and GitHub Actions.
• Familiarity with tools such as Datadog for observability and Snowflake for analytics.

Life at Flex

Building a successful company takes a diverse team of intelligent, curious, determined, empathetic, and self-aware people. Our headquarters is in New York City, with employees across the US, Australia, Canada, and South America. We’re growing quickly and deliberately, with a focus on building an inclusive culture. We value the perspectives our people bring and take 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

View our benefits and more at getflex.com/careers.