Backend Engineer

🕒 May 2

🇺🇸 United States – Remote

💵 $160k - $220k / year

⏰ Full Time

🟡 Mid-level

🟠 Senior

🔙 Backend Engineer

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Flex

WebsiteLinkedInAll Job Openings

11 - 50 employees

Founded 2023

💳 Fintech

☁️ SaaS

🤝 B2B

Fintech • SaaS • B2B

Flex is a SaaS payments infrastructure company that enables merchants and brands to accept HSA/FSA and other health-benefit payments. Its API-first platform integrates with e-commerce platforms (Shopify, WooCommerce, etc. ) and supports complex flows like split-card payments, subscriptions, eligibility verification, automated Letters of Medical Necessity, and enterprise-scale reporting to boost conversion and average order value. Flex is aimed at health, wellness and fitness brands that want to unlock pre-tax benefit spend at checkout while staying compliant.

📋 Description

• Design, build, and own backend services and APIs that power Flex’s applications • Model the domain - eligibility rules, transactions, merchants, consumer accounts, etc. - in data structures and APIs that other teams build on • Partner with frontend, design, and business stakeholders to translate merchant and consumer needs into reliable APIs and workflows • Own and improve backend service architecture, data models, and integrations • Analyze, troubleshoot, and resolve production issues rooted in business logic, data correctness, and transactional edge cases • Collaborate on cross-functional projects that connect the full Flex experience, from consumer checkout to merchant analytics • Create and maintain documentation for APIs, services, and on-call runbooks • Contribute to a culture of learning, problem-solving, and operational excellence

🎯 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 and always keeps the end user in mind • Proficient at leveraging AI tools to ship faster • Nice to have: Experience with building systems using Rust and background in payments, fintech, or health benefits (HSA/FSA), or another regulated, money-moving domain.

🏖️ Benefits

• Competitive compensation and equity package • Flexible, remote-friendly work environment