Job Overview
Location
United States
Job Type
Full-time
Category
Backend Engineer
Date Posted
May 3, 2026
Full Job Description
đź“‹ Description
- • Backend Engineer at Withflex Inc. responsible for designing and owning the services and APIs that power Flex’s platform, enabling health and wellness brands to accept HSA and FSA payments online.
- • Day-to-day responsibilities include building backend services and APIs, modeling domain logic (eligibility rules, transactions, merchant and consumer accounts), partnering with frontend, design, and business teams to translate needs into reliable systems, owning and improving backend architecture and data models, troubleshooting production issues related to business logic and transactional edge cases, contributing to cross-functional projects connecting checkout to merchant analytics, creating and maintaining API documentation and on-call runbooks, and fostering a culture of learning and operational excellence.
- • Withflex Inc. is an early-stage fintech company backed by First Round, Core VC, and Rethink Capital, solving the problem of HSA/FSA payment processing for merchants by enabling real-time eligibility verification, split payments, and Letter of Medical Necessity issuance at checkout—unlocking $150B in annual spending potential for consumers and brands like Equinox, Dermstore, Therabody, and Ultrahuman.
- • In this role, you will gain deep expertise in building scalable, reliable financial systems in a regulated domain, strengthen your skills in API design and data modeling, gain end-to-end ownership of critical payment infrastructure, and grow your impact in a high-trust, mission-driven environment where your work directly shapes company growth and consumer access to healthcare benefits.
🎯 Requirements
- • 5+ years of experience building production backend services and APIs in a typed language (Rust, TypeScript/Node, Go, Python, etc.)
- • Strong relational database fundamentals and experience designing APIs that other teams or external partners depend on
- • Resourceful, curious, and comfortable learning new tools quickly
- • Thrives in fast-paced, dynamic environments and enjoys wearing multiple hats
- • Collaborative and enjoys working across teams to solve problems
- • Execution mindset with a focus on the end user
- • Proficient at leveraging AI tools to ship faster
Skills & Technologies
About Withflex Inc.
Withflex is a technology company focused on revolutionizing the way businesses manage their flexible workforce. Their platform provides a comprehensive solution for hiring, onboarding, managing, and paying contingent workers, freelancers, and contractors. By centralizing these processes, Withflex aims to streamline operations, ensure compliance, and reduce administrative overhead for companies. They cater to businesses of all sizes looking to leverage flexible talent efficiently and effectively, offering tools for talent sourcing, contract management, time tracking, and automated payments. Withflex operates within the HR tech and gig economy enablement sectors.
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