Senior Backend Engineer - Sell Online

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 a vast set of simple and affordable business tools to help them start, run, and grow their businesses. Today, over 4 million businesses in 36 markets rely on SumUp as their financial partner to manage payments, finance and customer relationships.

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. Our focus is on Online Store and Bookings, two products at the heart of SumUp’s ecosystem. Together, they give merchants the power to manage appointments, showcase their offerings, and get paid—all from their phones.

We’re a cross-functional team of Product Managers, Designers, and Engineers who move fast, collaborate openly, and care deeply about crafting beautiful, performant mobile experiences. As part of this team, you’ll help us expand into new verticals, close the feature gap, enabling us to position our product as a complete and competitive solution for small merchants, and make digital selling effortless for small businesses everywhere.

What You’Ll Do

• Design, build, and maintain scalable backend systems supporting SumUp’s Bookings product
• Collaborate with frontend and mobile engineers to deliver new features and improve APIs across web, iOS, and Android
• Participate in technical planning, code reviews, and design discussions to ensure clean, testable, and maintainable code
• Continuously optimise performance, ensure observability, and uphold our high reliability standards
• Actively contribute to shaping the technical roadmap for the Sell Online platform

You’Ll Be Great For This Role If

• You have 5+ years of professional backend engineering experience
• You’re fluent in Kotlin (or Java) and have deep experience with Spring Boot
• You’ve worked with PostgreSQL, Kafka, Docker, Kubernetes, and AWS
• You understand RESTful APIs, distributed systems, and event-driven architectures (e.g. CQRS, Event Sourcing)
• You bring experience with CI/CD pipelines, GitHub Actions, and observability tools like Grafana or Honeycomb
• You thrive in collaborative teams, enjoy mentoring peers, and care about delivering real value to merchants(Nice to have) Familiarity with gRPC, Protobuf, or performance optimisation at the backend/database level

Why You Should Join Sumup (Warsaw) 🇵🇱

• 🌎 Opportunity to work , from our vibrant Warsaw office with inspiring art-filled lounges and a skyline terrace in the Mennica Legacy Tower. 
• 🌈 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 VSOP program: you will own a stake in SumUp’s future success 
• 🚴 Fitness support: work out on-site at our gym or explore the city using the Multisport Card, subsidised by SumUp for access to sports facilities across Warsaw 
• 🩺 Commitment to well-being: access health insurance coverage for you and your family, plus life insurance to further protect your peace of mind 
• 💰 PPK (Employee Capital Plan): grow your savings with joint contributions from SumUp and the State. 
• 🏖️ Generous time off: enjoy 26 days of paid leave plus public holidays and special leave days 🌴 Break4me: 1-month sabbatical after 3 years of service 
• 🔗 Referral Bonus: earn additional rewards by referring talented individuals to join the SumUp team

Job Application Tip

We recognise that candidates feel they need to meet 100% of the job criteria in order to apply for a job. Please note that this is only a guide. If you don’t tick every box, it’s ok too because it means you have room to learn and develop your career at SumUp.