Senior Backend Engineer - Kotlin, 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 owns the systems that power card issuing, and transaction processing for merchants across Europe, handling millions of transactions every day. We're scaling these systems to support new product capabilities and lay the foundations for a more global, resilient platform, and we're looking for a senior backend engineer who can take real ownership of this complex, high-throughput work while raising the technical bar for the rest of the squad.

It's a chance to shape distributed systems architecture at scale, mentor engineers around you, and build infrastructure that genuinely matters to small businesses.

🎥 Join us in our Sofia Team - get a feel for our Sofia office here.

What you'll do

• Own and drive the end-to-end delivery of backend services within the Cards EU domain, including observability, testing, and production support
• Lead architectural discussions and shape the technical roadmap by proposing solutions for complex, distributed systems challenges
• Partner with engineers in adjacent squads and the product manager to shape and refine the squad backlog
• Mentor engineers through code and design reviews, pragmatic technical trade offs, and knowledge sharing that raises the team's engineering standards
• Participate in incident reviews and the on-call rotation, taking accountability for the reliability of the services the team builds
• 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…

• Proven track record delivering production-ready backend services end to end, including testing, monitoring, and incident response, on a modern cloud-native stack.
• Production experience with Kotlin and genuine curiosity about picking up additional languages such as 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
• Take ownership of ambiguous problems and turn them into clear, scalable, and maintainable solutions.
• 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 connecting directly to Joliot-Curie metro station
• 🌴 Break4me: 1-month sabbatical after 3 years of service
• 🔗 Referral Bonus: earn additional rewards by referring talented individuals to join the SumUp team

About SumUp

Be empowered to do more that matters.

At SumUp, we're on a mission to empower small businesses across the globe by providing simple and affordable tools that allow them to thrive. Today, over 4 million businesses in 37 markets rely on SumUp as their financial partner to manage payments, finance and customer relationships.

Our commitment to small businesses is reflected in our diverse team of over 3,000 SumUppers from over 90 nationalities, united by global collaboration and an innovative mindset. Our core values lay the foundation for who we are and what we stand for, shaping our work culture and driving our success. We foster inclusivity and a continuous learning culture, providing a safe space for personal and professional growth. Our differences make us unique and strong as we strive to create an environment where everyone belongs and feels supported, no matter how they identify.

SumUp is proud to be an Equal Employment Opportunity employer, actively seeking and embracing diversity in our workforce. We don't make hiring or employment decisions based on race, colour, religion or religious belief, ethnic or national origin, nationality, sex, gender, gender identity, sexual orientation, disability, age or any other basis protected by applicable laws or prohibited by company policy. Our commitment extends beyond recruitment to creating a safe and respectful workplace where harassment of any form is strictly prohibited. Discover more about our culture and opportunities on our careers website, and follow our journey on LinkedIn, Instagram, and TikTok.