Senior Backend Engineer

<h3><strong>Salary range: 18 850 - 29 660 PLN per month</strong></h3> <h3><strong>About SumUp</strong></h3> <p>Be empowered to do more that matters.</p> <p>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.</p> <h3><strong>About the Team</strong></h3> <p>You’ll join the<a href="https://www.sumup.com/en-gb/online-store/"> <strong>Sell Online Tribe</strong></a>, 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, <strong>sell their products and services anywhere</strong>. 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.</p> <p>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.</p> <h3><strong>What You’ll Do</strong></h3> <ul> <li>Design, build, and maintain <strong>scalable backend systems</strong> supporting SumUp’s Bookings product</li> <li>Collaborate with <strong>frontend and mobile engineers</strong> to deliver new features and improve APIs across web, iOS, and Android</li> <li>Participate in <strong>technical planning, code reviews, and design discussions</strong> to ensure clean, testable, and maintainable code</li> <li>Continuously <strong>optimise performance</strong>, ensure observability, and uphold our high reliability standards</li> <li>Actively contribute to shaping the <strong>technical roadmap</strong> for the Sell Online platform<br><br></li> </ul> <h3><strong>You’ll Be Great for This Role If</strong></h3> <ul> <li>You have 5+ years of professional backend engineering experience</li> <li>You’re fluent in Kotlin (or Java) and have deep experience with Spring Boot</li> <li>You’ve worked with PostgreSQL, Kafka, Docker, Kubernetes, and AWS</li> <li>You understand RESTful APIs, distributed systems, and event-dr