
Tonsser · Berlin
ABOUT TONSSER Tonsser is on a mission to redefine youth sports. Hundreds of thousands of young athletes across Europe already use Tonsser to track their perfor...
Tonsser is on a mission to redefine youth sports. Hundreds of thousands of young athletes across Europe already use Tonsser to
track their performance, get discovered, and feel part of something bigger than the next match. We're now starting our most
ambitious chapter yet, a new project that will reshape an entire category, and we're looking for a Lead Backend Engineer to help
us build it.
SENIOR BACKEND ENGINEER — GLOBAL EXPANSION ABOUT THE TEAM The Global Expansion Acquiring Squad is the engine behind SumUp'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. WHAT YOU'LL DO * 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 YOU'LL BE GREAT FOR THIS ROLE IF… * 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 WHY YOU SHOULD JOIN SUMUP * 🌎 Opportunity to work with SumUppers 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 SumUp'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 SumUp team ABOUT SUMUP Be empowered to do more that matters. At SumUp, we're on a mission to empower small businesses across the globe by providing simple and affordable tools that allow them to thrive. Today, over 4 million businesses in 37 markets rely on SumUp as their financial partner to manage payments, finance and customer relationships. Our commitment to small businesses is reflected in our diverse team of over 3,000 SumUppers from over 90 nationalities, united by global collaboration and an innovative mindset. Our core values lay the foundation for who we are and what we stand for, shaping our work culture and driving our success. We foster inclusivity and a continuous learning culture, providing a safe space for personal and professional growth. Our differences make us unique and strong as we strive to create an environment where everyone belongs and feels supported, no matter how they identify. SumUp 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. Discover more about our culture and opportunities on our careers website, and follow our journey on LinkedIn, Instagram, and TikTok. 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.
ABOUT TALON.ONE: Talon.One is the most powerful incentives engine that unifies loyalty, promotions and gamification into one holistic platform. Backed by enterprise-grade security and scalability, Talon.One empowers companies to build personalized, profitable promotions and loyalty programs using any data. Today, over 250 of the world’s most-loved brands including Adidas, Sephora and Carlsberg work with Talon.One to drive deeper engagement and lasting loyalty with their customers. ABOUT THE TEAM: Our development team consists of specialists in frontend, backend, QA, product, and visual design. We work in small cross-functional teams that give everybody insight and hands-on experience of what everyone else is doing. Each team is self-sustained, autonomous, and responsible for a specific feature or area in our platform. We believe in strong collaboration, open communication, and mentoring to allow bi-directional growth. We are working to make Talon.One an inclusive workplace because we believe it is the right thing to do and because we want to have a positive impact on the entire tech industry. We are currently looking for a Senior Backend Engineer to join our development teams. You will work closely with our product people to design the right solutions to our challenging problems while collaborating, mentoring, and supporting the other team members. For this position, we need professionals who are already based in Berlin or willing to move to Berlin. ONCE YOU ARE HERE YOU WILL: * Be a crucial member in a small cross-functional team (a squad) * Collaborate closely with Product Manager and Tech Lead during roadmap discussions * Contribute effectively during all Scrum rituals, facilitation of process maturity increments, and engineering best practices initiatives * Provide valuable inputs during Refinement and Solution Design sessions and be able to lead feature development independently * Regularly participate in code reviews and provide constructive feedback * Consistently monitor the maintenance of quality standards and proactively recommend engineering or process improvements * Offer technical/soft guidance to Junior engineers and participate in Mentorship Programs * Participate in cross-squad (Backend Guild) brainstorming sessions and problem-solving discussions * Propose and own technical initiatives toward performance/scale/maintenance improvements WHAT WE NEED YOU TO BRING TO THE TABLE: * 6+ years of previous experience as a Backend Developer with focus on Golang * In-depth knowledge of REST API design, PostgreSQL, and Testing Techniques * Experience building scalable, maintainable, and performant large-scale applications * Experience designing and developing complex architectures, including monolithic and microservice architecture * Strong tendency towards implementing modern best practices like pair-programming sessions, unit and integration tests, adaptation of AI and automation, refactoring, SOLID principles, security best practices, documentation as code, regular knowledge sharing, etc. * Big-picture thinking; You collaborate with non-developers to clarify requirements and help plan projects, with an eye on the overall impact on the business & product * Proactive and constructive approach to support/mentor junior members of the team * A willingness to learn about and contribute to the whole stack is essential * A team-first attitude; As a group, we strive to leave egos at home * Empathy for your customers and your colleagues ABOUT TECHNOLOGY: * Kubernetes running on Google Cloud * PostgreSQL * We use Go for our API, core logic, and internal tooling * TypeScript, React, Redux, and CSS modules for our web application * Cypress for automated end-to-end testing * Other odds & ends in JavaScript and shell script WHAT'S IN IT FOR YOU: * A Research and Development Department of 90+ of engineers, product managers and product designers in Berlin * Leaders with 8+ years of experience building our promotions engine * €1,000 annual learning budge and free German language courses to boost your skills * 30 days of annual leave, plus extra paid days for your birthday and moving day * Home office setup budget, a monthly home office allowance * Freedom to work from abroad for up to 90 days worldwide! * Mental health support with nilo.health and a discounted Urban Sports Club membership * 20% company subsidy on your pension contributions * Subsidised BVG public transport ticket and a dog-friendly Berlin office where your furry friend is welcome * Lease your ideal bike through BusinessBike
ABOUT TALON.ONE: Talon.One is the most powerful incentives engine that unifies loyalty, promotions and gamification into one holistic platform. Backed by enterprise-grade security and scalability, Talon.One empowers companies to build personalized, profitable promotions and loyalty programs using any data. Today, over 250 of the world’s most-loved brands including Adidas, Sephora and Carlsberg work with Talon.One to drive deeper engagement and lasting loyalty with their customers. ABOUT THE TEAM: Our development team consists of specialists in frontend, backend, QA, product, and visual design. We work in small cross-functional teams that give everybody insight and hands-on experience of what everyone else is doing. Each team is self-sustained, autonomous, and responsible for a specific feature or area in our platform. We believe in strong collaboration, open communication, and mentoring to allow bi-directional growth. We are working to make Talon.One an inclusive workplace because we believe it is the right thing to do and because we want to have a positive impact on the entire tech industry. We are currently looking for a Senior Backend Engineer to join our development teams. You will work closely with our product people to design the right solutions to our challenging problems while collaborating, mentoring, and supporting the other team members. For this position, we need professionals who are already based in Berlin or willing to move to Berlin. ONCE YOU ARE HERE YOU WILL: * Lead and deliver features of any size — independently or by coordinating effort across the squad * Drive technical discovery and solution design in collaboration with your PM and Tech Lead * Actively share technical knowledge across the Backend Guild — through discussions, documentation, and knowledge-sharing sessions * Participate in cross-squad (Backend Guild) brainstorming sessions and problem-solving discussions * Mentor and unblock junior and mid-level engineers through pairing, code review, and deliberate feedback * Champion improvements to quality, maintainability, and engineering process within your squad and beyond * Be a crucial member in a small cross-functional team (a squad) * Contribute effectively during all Scrum rituals, facilitation of process maturity increments, and engineering best practices initiatives * Regularly participate in code reviews and provide constructive feedback * Consistently monitor the maintenance of quality standards and proactively recommend engineering or process improvements WHAT WE NEED YOU TO BRING TO THE TABLE: * 6+ years of experience as a Backend Developer building enterprise-grade web applications — Go strongly preferred, but we're also open to strong backgrounds in other mainstream backend languages (e.g., Node.js, Java, C#, Python). * Basic working familiarity with Go — you don't need deep expertise, but you should be comfortable reading Go code and understanding its core syntax and idioms. * If your background is primarily in another stack: during interviews, you'll need to demonstrate you can pick up Go quickly and show a genuine willingness to build your career in Go — our backend stack (Go) isn't changing, so this is a hard requirement, not a nice-to-have. * Strong architectural instincts — you understand tradeoffs and can articulate them clearly to technical and non-technical stakeholders * The ability to mentor others without being asked — you notice where people are stuck and act on it * A guild mindset: you contribute to backend-wide discussions, not just your squad's backlog * In-depth knowledge of REST API design, PostgreSQL, and Testing Techniques * Experience building scalable, maintainable, and performant large-scale applications * A proven track record of designing the architecture of multiple applications or complex features end-to-end * Hands-on experience owning maintenance, performance, and security concerns for production systems * Strong tendency towards implementing modern best practices like pair-programming sessions, unit and integration tests, adaptation of AI and automation, refactoring, SOLID principles, security best practices, documentation as code, regular knowledge sharing, etc. * Big-picture thinking; You collaborate with non-developers to clarify requirements and help plan projects, with an eye on the overall impact on the business & product * A willingness to learn about and contribute to the whole stack is essential * A team-first attitude; As a group, we strive to leave egos at home * Empathy for your customers and your colleagues ABOUT TECHNOLOGY: * Kubernetes running on Google Cloud * PostgreSQL * We use Go for our API, core logic, and internal tooling * TypeScript, React, Redux, and CSS modules for our web application * Cypress for automated end-to-end testing * Other odds & ends in JavaScript and shell script WHAT'S IN IT FOR YOU: * A Research and Development Department of 90+ of engineers, product managers and product designers in Berlin * Leaders with 8+ years of experience building our promotions engine * €1,000 annual learning budget and free German language courses to boost your skills * 30 days of annual leave, plus extra paid days for your birthday and moving day * Home office setup budget, a monthly home office allowance * Freedom to work from abroad for up to 90 days worldwide! * Mental health support with nilo.health and a discounted Urban Sports Club membership * 20% company subsidy on your pension contributions * Subsidised BVG public transport ticket and a dog-friendly Berlin office where your furry friend is welcome * Lease your ideal bike through BusinessBike