Staff Software Engineer, Fullstack-MarTech

Flex•San Francisco, NY

1d•Hybrid

About The Position

Flex is a growth-stage, NYC headquartered FinTech company that is creating the best rent payment experience. 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. We are looking for motivated individuals to help us keep our mission growing. 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.

Requirements

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).
Excellent written and verbal communication skills, with experience in cross-functional collaboration — especially translating between marketing goals and engineering tradeoffs.
Proven experience building high-quality, high-performance web and mobile UIs to spec — including responsive, SEO-conscious, conversion-optimized pages.
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, webhooks, message queues, event-driven design, and scalable architectures.
Experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB) and containerization tools.
Comfort integrating and debugging third-party APIs and SDKs where you don't control the contract, including rate limits, partial failures, and reconciliation.

Nice To Haves

Experience on a growth, marketing engineering, or MarTech team.
Hands-on experience with platforms such as Braze, Singular/AppsFlyer/Branch, Google Tag Manager, Amplitude, LaunchDarkly, or the Meta/Google/TikTok/Apple ad and conversion APIs.
Familiarity with attribution, identity resolution, and conversion tracking, and the privacy constraints they operate under (consent management, state privacy laws, platform tracking restrictions).
Experience with A/B testing and experimentation frameworks, web performance optimization, and headless/CMS content tooling.
Experience with big data platforms and tooling, including Snowflake.
Proficient in CI/CD systems (preferably GitHub Actions), git, and automation; observability tools such as DataDog; and Infrastructure as Code using CDK or Terraform.
Skilled at elevating team standards through best practices and mentoring junior engineers.

Responsibilities

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.
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.