Senior Full Stack Engineer - Checkout & Payments

This position is listed on behalf of a partner company, who manages all applications and next steps. Our partner is looking for a Senior Full Stack Engineer - Checkout & Payments based in the United States. This is a senior full stack engineering role focused on building a world-class consumer checkout and payments experience. You’ll own substantial, user-facing initiatives from concept through launch, working in a small team of highly experienced engineers with significant autonomy. The role combines modern frontend engineering with backend APIs, data models, and payment infrastructure. You’ll partner closely with Product, Marketing, and Design to shape experiences that improve conversion and make complex healthcare spending simple for consumers. Performance, experimentation, and data-driven decision-making will be central to your work. You’ll also help establish frontend standards and technical practices as the platform scales. Own large, user-facing product initiatives from initial concept and technical design through implementation, launch, measurement, and iteration. Collaborate closely with Product, Marketing, and Design to define the direction of the consumer web experience and translate business objectives into high-quality technical solutions. Build and optimize modern frontend experiences using technologies such as Next.js, React, TypeScript, and Tailwind. Establish and evolve frontend engineering standards, patterns, and development practices across the team. Improve website performance by analyzing rendering behavior, page-load characteristics, Core Web Vitals, and other relevant performance metrics. Develop scalable frontend architecture using component libraries, monorepos, headless CMS platforms, and other modern web development approaches. Design, build, and expand backend APIs and data models that support important product and checkout initiatives. Work across the full technology stack, investigating issues and opportunities from the user interface through backend services and data layers. Experiment with product experiences and use quantitative data to evaluate results, improve conversion, and guide product decisions. Contribute to checkout and payment-related infrastructure, with an opportunity to shape reliable and intuitive payment experiences. Partner with other senior engineers to maintain high technical standards while operating with significant autonomy and ownership. Help evolve the engineering architecture and technical foundation as the product and consumer base continue to grow. Requirements Senior-level software engineering experience on high-performing engineering teams, with strong expertise in modern frontend development. Advanced experience with Next.js, React, TypeScript, Tailwind, or comparable technologies. Strong understanding of frontend rendering behavior, particularly within frameworks such as Next.js, and demonstrated ability to optimize page-load performance. Practical experience using Core Web Vitals and related performance metrics to identify and resolve frontend performance issues. Experience building and maintaining large-scale frontend applications using concepts such as component libraries, monorepos, and headless CMS platforms. Strong backend development experience with Python, Django, or comparable technologies. Experience designing, consuming, and extending backend APIs and data models. Ability and willingness to work across the entire stack, from polished user interfaces through backend services and data infrastructure. Strong product mindset and interest in experimentation, conversion optimization, and data-driven decision-making. Excellent communication and collaboration skills, with the ability to work effectively with Product, Marketing, Design, and Engineering stakeholders. Comfortable operating autonomously, taking ownership of ambiguous problems, and driving initiatives from inception to completion. Experience with payment systems or payment infrastructure is a strong