Fullstack Engineer

Sum Up gives small businesses the tools they need to get paid, manage their money, and grow - today, over 4 million merchants across 37 markets worldwide rely on Sum Up to do exactly that.

The Bank Web squad sits within Sum Up's Bank domain and owns the web experience across our banking surfaces - from the business account dashboard that merchants use daily, to the back‑office tooling that powers the support teams behind them. The team has a clear mission: make Bank Web a genuinely first‑class platform, on par with our mobile applications in quality, reliability, and performance.

Joining now means being part of a team that’s at a key growth point – modernization work, growing scope across markets, and making architectural decisions that will shape how millions of merchants experience Sum Up's banking products.

• Build and own features end-to-end across our web banking surfaces – from scoping and component implementation through testing, observability, and production maintenance
• Work across the full stack – including defining API contracts, working with backend proxies, and integrating with the services that power our banking platform
• Contribute to modernisation efforts, including architectural improvements, component refactoring, and stack migrations that reduce technical debt and accelerate future delivery
• Review peers' pull requests with attention to UI consistency, accessibility, and frontend best practices
• Participate in production support and incident reviews, helping to strengthen the squad's operational resilience across its web domain

• Strong experience with React, Type Script, with a track record of delivering production-ready features end-to-end – not just isolated UI components
• Genuine full-stack capability:
  Experience defining API contracts, working with backend proxies, and owning integrations, not just consuming them; backend experience in Node, Kotlin, Java, or Golang is valued
• Solid understanding of frontend architecture, component design patterns, state management, and how frontend applications connect to backend services
• Experience writing and maintaining frontend tests (unit, integration, snapshot, end-to-end) and a genuine care for code quality and reliability
• Comfort navigating a complex, multi-stack codebase. React and Type Script are core to this role, while our broader ecosystem also includes Node.js, Kotlin, Java, Go, Angular, AWS and Kafka. Prior experience with all of these is not required, but familiarity with most of them is a plus
• Curiosity about complex domains – banking products have intricate user flows and edge cases, and you enjoy digging into them to find the right solution
• Familiarity with CI/CD practices and getting changes safely to production; exposure to AI tooling to augment engineering workflows is a plus

• Opportunity to work with Sum Uppers globally on large-scale fintech products used by millions of businesses worldwide, from our modern Sofia office. This involves an office-first setup
• 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 Virtual Stock Option programme: you will own a stake in Sum Up's future success
• A dedicated annual L&D budget of €2000 and 10 paid days of educational leave which can be used to attend conferences and/or advance your career through further education
• Generous time off: 25 days of paid leave, plus one extra day per year of service (up to 35), along with public holidays and special leave options
• Peace of mind: additional health insurance and life insurance
• Stay active:
  
  on-site yoga and a co-sponsored Multisport card offering access to hundreds of sports facilities
• Meal support: benefit from a tax-free food voucher program plus flexibility via our Re:
  
  Benefits platform
• Easy commute: free shuttle buses connecting directly to Joliot-Curie metro station
• Break4me: 1-month sabbatical after 3 years of service
• Referral Bonus: earn additional rewards by referring talented individuals to join the Sum Up team

Sum Up is proud to be an…