Senior Full Stack Engineer - Payments (Remote)

OutsideHire

8d•Remote

About The Position

OutsideHire is seeking a Senior Full Stack Engineer to join their team. This role involves building across the payments platform, including the embeddable SDK for collecting credentials, services for session creation and transaction routing, tokenization boundaries, and webhook and reconciliation flows. The position focuses on infrastructure that handles real money, where accuracy and reliability are paramount. The engineer will work on both the client and server sides of the payment process.

Requirements

7+ years of experience building production software across frontend and backend.
Strong proficiency in React and TypeScript, including understanding rendering behavior, state boundaries, effect lifecycles, and component API design.
Strong backend development skills, particularly in .NET, with the ability to design services, reason about API contracts, debug across the stack, and participate in architecture discussions.
Experience with payment systems, including gateway APIs, tokenization, hosted fields, webhooks, and reconciliation, or equivalent work in a domain where correctness is critical.
Solid understanding of security fundamentals, including same-origin policy, CSP, CORS, XSS vectors, iframe isolation, token handling, and client-side security best practices.
Experience using AI tools like Claude Code, Cursor, or Codex as a daily driver.
A strong testing discipline, recognizing the liability of untested payment code.

Nice To Haves

Java, Kotlin, and Quarkus experience.
Hands-on experience with gateway and tokenization stacks.
Experience with PCI DSS scope reduction and SAQ A or SAQ A-EP work.
3D Secure 2 implementation experience.
Cloud and DevOps exposure (Azure or AWS).
CI/CD ownership experience.

Responsibilities

Build the payment SDK and client layer, including hosted-fields integration with iframe isolation and a gateway-agnostic API.
Develop the payment services, focusing on session intent, gateway routing, tokenization, idempotency, HMAC-signed request flows, and webhook/reconciliation logic.
Enhance the platform by implementing versioning and deprecation strategies, ensuring observability across the payment path, and improving the developer experience for engineers integrating with the system.
Write tests to ensure the reliability and correctness of payment code.
Collaborate with product and client stakeholders.
Ask clarifying questions and escalate ambiguity early.
Push back on incorrect approaches with better alternatives.
Contribute to architecture discussions.
Read gateway documentation thoroughly.