At SumUp, we empower millions of small businesses worldwide. Our Payments Tribe is at the heart of this mission, processing billions of transactions across 36+ countries each year. We're building reliable, secure, and scalable systems that truly make a difference. THE TEAM:  Our robust payments processing platform has powered SumUp’s global business for over a decade. The Online Payments team, now a key part of our Payments Tribe, is responsible for facilitating all Card Not Present (CNP) transactions, ensuring our merchants can accept payments seamlessly online. This entire ecosystem is developed in Sofia by autonomous, cross-functional, and co-located squads, each owning their part of the platform end-to-end. We are currently in an exciting phase of scaling and improving existing products, while also developing innovative new ones. You'll make a significant impact by improving and co-creating our existing and new microservices architecture platforms, tackling complex scaling and new development challenges. Scalability and high availability are always at the forefront of our work. You'll join a team that values solid engineering and impactful solutions. You'll contribute to the design and development of our Golang-based Online Payments platform, working with cutting-edge tech and directly influencing our product. OUR TECH STACK:  We believe in using the best technology for each challenge, fostering an environment of continuous learning and exploration. Our current ecosystem includes Golang, Kafka Streams, PostgreSQL/RDBMS, AWS, microservices architecture. WHAT YOU'LL DO: * Co-design and develop high-performance, secure backend services for our Online Payments Platform  * Participate in API design and implementation for both internal and external integrations. * Deliver business value through backend decisions and active participation in product discussions. * Ensure high code quality, comprehensive test coverage, and clear documentation. * Optimize application performance and scalability through active monitoring and proactive solutions. * Collaborate closely with other software developers, QA, and DevOps engineers for smooth deployment, continuous integration, and support. * Actively participate in code reviews, fostering a culture of continuous improvement. YOU'RE A GREAT FIT IF YOU HAVE: * Solid experience as a Backend Software Engineer in any modern language(e.g. Go, Java, Python, Kotlin, etc.). We care more about how you think and design systems than the specific language you use. * Experience with PostgreSQL/RDBMS and distributed, fault-tolerant systems. * A genuine passion for clean, maintainable, and testable code. * Interest in using AI as part of your development workflow. * A good understanding of software architecture and application design. * Bonus points for: Experience with Docker and/or Kubernetes, Kafka/other messaging systems, Unix/Linux environments, and DevOps practices (CI/CD). WHY JOIN SUMUP? * Make an impact on a global scale - our systems serve millions of merchants * Learn from experienced engineers while working on complex, real-world problems * Be part of a tech-agnostic team that uses the right tools for the job * Collaborate with SumUppers worldwide on large-scale fintech products used by millions, based in our Sofia office (office-first setup). * Access a €2,000 annual L&D budget to attend conferences or advance your career through education. * Enjoy 25 days of paid leave (increasing with tenure), plus paid vacations for special occasions and a 1-month sabbatical every 3 years. * Benefit from extra perks like health and life insurance, co-sponsored Multisport cards, childbirth/adoption bonuses, discounts, a referral program, 100 EUR monthly food vouchers, 40 EUR flexible benefits, and more. Please note: This role requires the right to work in Bulgaria. We are currently not able to support visa applications or relocation for this position at this time. About us: SumUp is a leading financial technology company, founded in 2012 with the goal of empowering small businesses around the globe. We’re the financial partner of choice for more than 4 million merchants in over 35 markets. We collectively build, plan and fine-tune the technology that drives SumUp and empowers small businesses around the world. We believe in the everyday hero. Those who have the courage to follow their passion and who have the strength and determination to realise their dreams. Small business owners are at the heart of all we do, so we're creating powerful, easy-to-use financial solutions to help them run their business. With a founder's mentality and a 'team-first attitude' our diverse teams across Europe, South America, and the United States work together to ensure that small business owners can be successful doing what they love. SumUp is an Equal Employment Opportunity employer that proudly pursues and hires a diverse workforce. SumUp does not make hiring or employment decisions on the basis of 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. SumUp also strives for a healthy and safe workplace and strictly prohibits harassment of any kind.   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.