Senior Backend Engineer - Cards

SumUp builds simple, affordable financial tools that help small businesses get paid, manage their money, and grow. Beyond payments, we offer a number of financial products - including business banking, card products, lending, and invoicing — giving merchants everything they need to manage their payments and finances in one place. The Cards squad is a core part of that, owning the systems that power card issuing, lifecycle management, and transaction processing for merchants across Europe. We handle millions of card transactions every day, and we're now scaling those systems to support new product capabilities while laying the foundations for a more global, resilient platform. That's why we're growing the team and looking for a seasoned backend engineer who can take real ownership of complex, high-impact work. If you want to build systems that genuinely matter to small businesses and you're excited by the technical depth that comes with high-throughput, distributed architecture, this is the role for you. 🎥 Join us in our Sofia Team - get a feel for our Sofia office here . What you'll do Own and lead the end-to-end delivery of backend services within the Cards EU domain, including observability, testing, and production support Contribute to the technical roadmap by participating in architectural discussions and proposing solutions for complex, distributed systems challenges Raise well-scoped pull requests, conduct thorough code reviews, and help maintain high standards of code quality and test coverage across the team Collaborate closely with engineers in adjacent squads and with the product manager to shape and refine the squad backlog Participate in incident reviews and the on-call rotation, taking accountability for the reliability of the services you build Apply and champion AI tooling to accelerate engineering workflows, and help raise the team's overall AI literacy You'll be great for this role if… Solid, hands-on experience delivering production-ready backend services end-to-end, including testing, monitoring, and maintenance, on a modern cloud-native stack Production experience with Kotlin and an openness to work with additional languages such as Elixir, Java or Golang. Solid understanding of distributed systems, API design, data modelling, and working with relational databases Hands on experience in containerisation, orchestration, and CI/CD practices Ability to take an ambiguous product problem, define the technical approach, and lead it through to implementation with minimal guidance Comfort working across teams and communicating clearly in written and spoken English in a professional setting Genuine curiosity about the product domain — comfortable applying a backend lens during feature refinement and thinking beyond the code to understand how your work shapes the user experience Why you should join SumUp 🌍 Opportunity to work with SumUppers globally on large-scale fintech products used by millions of businesses worldwide, from our modern Sofia office. 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 and 10 paid days of educational leave which can be used to attend conferences and/or advance your career through further education 🏖 Generous time off: 25 days of paid leave, plus one extra day per year of service (up to 35), along with public holidays and special leave options 🏥 Peace of mind: additional health insurance and life insurance 💪 Stay active: on-site yoga and a co-sponsored Multisport card offering access to hundreds of sports facilities 🍽 Meal support: benefit from a tax-free food voucher program plus flexibility via our Re:Benefits platform 🚌 Easy commute: free shuttle buses connect...