Senior Frontend Engineer – Sell Online

About the team You'll join the Sell Online Tribe, the group shaping how merchants bring their businesses to life online. We design and build tools that help millions of entrepreneurs, from barbers to bakers, sell their products and services anywhere. You'll 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, while also working on integration products that provide essential features used across many other SumUp products. They're high-traffic, high-responsibility products that other SumUp teams depend on too. You'll join a small, cross-functional team and take on genuine ownership of the frontend - not just executing tickets, but shaping how the products evolve. With new features to ship and integration products to keep secure and current, there's real, meaningful work to get stuck into from day one. What you'll do Build and maintain frontend features across payment links, gift cards, and online checkout products, writing clean, testable, and maintainable code Contribute to the development and upkeep of our integration products and SDKs, used by both internal teams and external partners Take part in technical planning, design reviews, and sprint ceremonies - bringing your perspective on estimations, trade-offs, and improvements Help reduce tech debt and improve application performance, observability, and accessibility as a foundation for future delivery Monitor live services and respond to issues, providing redundancy for customer support requests reaching the team You'll be great for this role if… You have 5+ years of experience in TypeScript and JavaScript, with hands-on experience building production-grade React and Next.js applications (including SSR and app router patterns) You have experience writing unit, integration, and end-to-end tests using tools like Jest, Vitest, or React Testing Library You're comfortable working within CI/CD workflows and collaborating in agile environments (Scrum or Kanban) You have experience with UI libraries such as Radix or shadcn, and a solid understanding of accessibility and UX best practices You have a product mindset - someone who cares about the value delivered to merchants, not just the code written to get there, and who can work autonomously to drive complex features end-to-end Why you should join SumUp 🌎 Opportunity to work in a truly global, multicultural team from our open, vibrant Cologne office, located in the heart of the city. This involves an office-first setup 🌈 Commitment to Diversity and Inclusion: be part of a workplace that values and promotes diversity, fostering an inclusive environment where everyone's perspectives are respected and embraced 🚀 Enrolment onto our Virtual Stock Option programme: you will own a stake in SumUp's future success 📚 A dedicated annual L&D budget of €2000 for your individual development, which can be used to attend confere