Senior Backend Engineer (Kotlin) - Cards
Senior backend engineer on SumUp's Cards squad in Sofia, owning services for card issuing, lifecycle management and transaction processing at scale. Day-to-day work spans Kotlin-based cloud-native microservices, distributed systems design, observability, code reviews and on-call.
- Compensation
- Not disclosed
- Location
- Sofia, Bulgaria
- Work setup
- Not specified
- Seniority
- Senior
- Employment
- Not specified
- Experience
- 3+ years
- Category
- Backend
- Posted
Skills
Must have
- Production experience with Kotlin
- Openness to work with additional languages such as Elixir, Java or Golang
- Hands-on experience delivering production-ready backend services end-to-end (testing, monitoring, maintenance) on a modern cloud-native stack
- Solid understanding of distributed systems, API design, data modelling, and working with relational databases
- Hands-on experience in containerisation, orchestration, and CI/CD practices
- Ability to take an ambiguous product problem, define the technical approach, and lead it through to implementation with minimal guidance
- Comfort working across teams and communicating clearly in written and spoken English
- Genuine curiosity about the product domain and thinking beyond the code to user experience
Full description
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