Staff Software Engineer, Martech

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 the role Flex is looking for a Staff Software Engineer to join our MarTech (Marketing Technology) team. This role involves spearheading the implementation of the platforms, services, and customer-facing web experiences that power how Flex finds, wins, and keeps customers. MarTech is the connective layer between our ad platforms, website, messaging systems, analytics, and product data. We turn marketing spend into a measurable, repeatable growth engine, and give marketing the ability to launch, test, and personalize campaigns without hand-built engineering each time. It's a team with a broad surface area, owning growth engineering end to end across Lifecycle Marketing (email & SMS), Performance Marketing (paid acquisition), Brand (social and every getflex.com property), and Product Marketing. Here are some of the projects and systems in MarTech you'll have opportunities to work on: Incentive platform — event-driven credit assignment for referrals, affiliates, and campaigns. Attribution and measurement — conversion APIs, identity resolution, and spend/event pipelines behind our acquisition cost reporting. Customer-facing web — the full getflex.com surface area and paid-acquisition landing pages. Lifecycle messaging — campaign orchestration, audience syncs, and event-driven notifications. What you'll do Build and own full-stack marketing services and web experiences that drive customer acquisition and retention. Design and develop 24/7 high-scale APIs, event-driven services, and data pipelines. Our stack runs on AWS: Java and Spring Boot for the existing backend code base; TypeScript and React for web. Build measurement into everything we ship, and integrate third-party ad, analytics, and messaging platforms behind durable abstractions. Work closely with marketing, data, product, design, and engineering peers to launch features and experiments across web and mobile. Qualifications Minimum Qualifications 8+ years of professional software development experience. 6+ years of hands-on experience with Java. 3+ years of experience with TypeScript. 3+ years of experience with React (or React Native), including modern architectures and tooling in the React ecosystem (Hooks, Components, Context, state management). …