Senior Backend Engineer - Global Expansion

Senior Backend Engineer — Global Expansion

About the team The Global Expansion Acquiring Squad is the engine behind the company's growth into new markets — integrating local payment acquirers, enabling merchant onboarding, and ensuring transactions flow reliably across countries like Mexico, Canada, New Zealand, and Australia. This role sits at the heart of that mission, owning critical backend systems while also shaping how the squad works — building AI agents and developer tooling that make the entire team faster and smarter.

If you're a backend engineer who wants real ownership, enjoys working in ambiguous and complex environments, and is genuinely excited about teaching AI how your codebase works (not just using it for autocomplete), this role is for you.

• Design and build scalable backend services in Golang and Kotlin, covering merchant onboarding, transaction processing, and reconciliation across multiple acquirers and markets
• Lead technical investigations for new market launches and mentor engineers on the team
• Configure and maintain AI coding assistants (Cursor, Copilot, Continue) with team-specific rules, framework conventions, and testing patterns — so generated code fits our systems, not generic templates
• Build AI agents that automate repetitive development tasks, such as generating integration stubs, updating OpenAPI specs, and flagging idempotency violations
• Keep documentation accurate and AI‑accessible, so the team spends less time answering "how does X work?" and more time shipping

• Strong proficiency in Golang (primary) or a JVM language such as Java or Kotlin, with experience building distributed, fault‑tolerant backend systems
• Experience configuring AI coding assistants at a team level — defining rules, prompts, and context packages that produce consistent, framework‑compliant output
• Solid understanding of idempotency, retry policies, and transaction safety in payment or financial systems
• Comfort working across multiple teams and domains simultaneously, navigating ambiguity and influencing without direct authority
• A track record of taking ownership in complex, cross‑functional environments where the scope isn't always clearly defined

• Opportunity to work with Sum Uppers globally on large‑scale fintech products used by millions of businesses worldwide, from our Berlin 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 the company's future success
• A dedicated annual L&D budget of €2,000 for your individual development, which can be used to attend conferences and/or advance your career through further education
• A corporate pension scheme where we match up to 20% of your contributions
• Generous time off: enjoy 28 days of paid leave plus public holidays and special leave days
• Numerous other benefits such as Urban Sports Club subsidy, Kita placement assistance, subsidised office lunches
• Break4me: 1-month sabbatical after 3 years of service
• Referral Bonus: earn additional rewards by referring talented individuals to join the company team

the company is proud to be an Equal Employment Opportunity employer, actively seeking and embracing diversity in our workforce. We don't make hiring or employment decisions based on 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. Our commitment extends beyond recruitment to creating a safe and respectful workplace where harassment of any form is strictly prohibited.