Senior Frontend Engineer - Sell Online

About the role

You will join the Sell Online Tribe, the group shaping how merchants bring their businesses to life online. You will design and build tools that help millions of entrepreneurs, from barbers to bakers, sell their products and services anywhere. You will be working on some of SumUp's biggest merchant-facing online products as part of the Bifrost team, contributing to growing and scaling critical products like Payment Links and Gift Cards. You will also work on integration products that provide essential features used across many other SumUp products, which are high-traffic and carry high responsibility. You will join a small, cross-functional team and take on genuine ownership of the frontend, shaping how the products evolve beyond merely executing tickets. With new features to ship and integration products to keep secure and current, there is real, meaningful work to get stuck into from day one.

Key facts

What you'll do

• Architect and implement robust frontend solutions for payment links, gift cards, and online checkout products, delivering clean, testable, and maintainable code that elevates the merchant experience.
• Drive the development and maintenance of integration products and SDKs, ensuring reliability for both internal teams and external partners who depend on these critical interfaces.
• Influence technical direction by actively participating in planning, design reviews, and sprint ceremonies, articulating trade-offs and proposing improvements that strengthen the product foundation.
• Champion the reduction of technical debt while enhancing application performance, observability, and accessibility, laying a solid groundwork for future delivery and scalability.
• Assume responsibility for monitoring live services and responding to incidents, providing redundancy and support for customer requests that reach the team.
• Collaborate with designers and product managers to translate complex requirements into intuitive, accessible, and high-performing user interfaces that merchants can rely on.
• Mentor junior developers by sharing best practices in testing strategies, component design, and frontend architecture, fostering a culture of craftsmanship within the team.
• Evaluate and integrate emerging frontend tools and libraries that align with SumUp's standards, ensuring the technology stack remains modern and efficient.
• Contribute to the documentation and knowledge-sharing initiatives that enable smooth onboarding and long-term maintainability of the codebase.
• Act as a quality advocate by writing and maintaining comprehensive test suites, including unit, integration, and end-to-end tests that instill confidence in releases.

Requirements

You must possess 5+ years of experience in TypeScript and JavaScript, with hands-on experience building production-grade React and Next.js applications, including Server-Side Rendering and App Router patterns. You must have experience writing unit, integration, and end-to-end tests using tools such as Jest, Vitest, or React Testing Library. You must be comfortable working within CI/CD workflows and collaborating effectively in agile environments that follow Scrum or Kanban methodologies. You must have experience with UI libraries such as Radix or shadcn, along with a solid understanding of accessibility and user experience best practices. You must demonstrate a product mindset, caring about the value delivered to merchants rather than just the code written to achieve it, and you must be able to work autonomously to drive complex features from conception to completion.

Practical notes

The role is based in Cologne, Germany, within a vibrant office-first environment situated in the heart of the city. This position involves standard working hours and requires adherence to the company's policies regarding attendance and collaboration. Travel requirements are minimal, as the focus remains on local execution within the established team structure. No specific visa requirements are outlined beyond standard German employment regulations. The application process follows internal timelines managed by the SumUp recruitment team, and interested candidates should expect coordinated communication regarding next steps through official channels.