Senior Backend Engineer (Golang) - Payments Infrastructure

SumUp enables businesses to get paid easily, process orders quickly, sell online instantly and manage their money more efficiently. We create the tools businesses need to make their business and their customer experience thrive. The payments processing platform, consisting of other sub-platforms, has powered SumUp’s global business for more than 10 years now. It’s developed in Sofia by the Payments Tribe, composed of several teams (squads). Each squad is cross-functional, autonomous and co-located, working on its part of the platform end-to-end. Now, we are taking a major step forward in our Payments journey: building our own acquiring capability in Europe. About the team You’ll join a growing Payments team working on the next generation of SumUp’s payment capabilities. The team is building and evolving foundational systems that will improve the reliability, scalability and flexibility of our products. This is an opportunity to work on a new and important area of our platform, where your technical decisions will help shape how SumUp supports millions of small businesses around the world. You’ll have the chance to contribute from an early stage, solve complex engineering challenges and see the impact of your work in real-world payment experiences. About the role As a Senior Software Engineer in our own acquiring team, you’ll help build and evolve the systems that power SumUp’s payment experiences. You’ll work on foundational, greenfield components that improve the reliability and scalability of our platform while enabling us to deliver new payment capabilities to small businesses around the world. This is an opportunity to influence architectural decisions, shape engineering practices and work on highly critical infrastructure from the ground up. What you’ll do: Design and build core acquiring capabilities, including authorisation, clearing and settlement processing. Develop the APIs, data models and services that will form the foundation of our acquiring platform. Build reporting, back-office and operational tools for a reliable day-to-day acquiring operation. Ensure our systems meet card-scheme, security and compliance requirements. Create strong observability, monitoring and incident-response foundations for an always-on payments platform. Work closely with teams across Processing, Reconciliation, Risk, Compliance, Finance and Treasury. Contribute to architecture discussions and make sound technical decisions in an ambiguous, evolving domain. Take ownership of medium-to-large technical initiatives that span multiple teams. Identify and help prioritise technical debt, operational risks and opportunities to improve the platform. Support the growth of the team through mentoring, code reviews and shaping testing and on-call practices. You’ll be great for this role if you have: 5+ years of professional software engineering experience, including hands-on experience with Go. Experience building and consuming APIs in production environments. Understanding of software architecture, design principles, data modelling, API design and SOLID principles. Experience working with SQL and NoSQL databases; experience with PostgreSQL and Kafka is valuable. Practical experience with Docker, AWS and Kubernetes. A DevOps mindset and an interest in building, operating and improving the systems you own. Strong problem-solving skills and the ability to investigate complex issues methodically. A collaborative approach and openness to feedback. A strong sense of ownership and accountability for your work. It would be a great advantage if you have: Experience with Elixir or another functional programming language. Experience with AWS Prometheus and Grafana. Experience in fintech, payments or another regulated domain. Knowledge of card schemes, acquiring, authorisation, clearing or settlement. You do not need to know the acquiring domain already. What matters is your technical foundation, curiosity and willingness to learn. You will work alongside colleagues who are building this capability together, with plenty of room to ask questions and make an impact. Why you should 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. About SumUp We believe in the everyday hero. Small business owners are at the heart of all we do, so we create powerful, easy-to-use financial solutions to help them run their businesses. 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 the small business owners we partner with 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, color, 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. SumUp will not accept unsolicited resumes from any source other than directly from a candidate. 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.