SumUp Backend Engineer interview questions & guide 2026

While the interview process is tailored to the specific team and seniority level, the following questions represent recurring themes found in the SumUp engineering evaluation process. Use these as a baseline to understand the types of challenges you will be asked to solve.

Technical & Domain Expertise

These questions assess your proficiency with core languages, specifically Golang, and your understanding of distributed systems.

• Explain the pros and cons of using Golang for high-concurrency microservices.
• How do you manage database migrations in a distributed environment without downtime?

Preparation at SumUp requires a focus on both depth of technical knowledge and breadth of architectural thinking. You should prepare to articulate not just "how" you solve a problem, but "why" you chose a specific trade-off.

Role-related knowledge – You must demonstrate a mastery of your primary programming language, with a strong preference for Golang fluency. Interviewers look for deep understanding of memory management, concurrency models, and standard library capabilities.

Problem-solving ability – SumUp interviewers favor candidates who can structure their thoughts clearly when faced with ambiguity. Always state your assumptions upfront and walk the interviewer through your decision-making process before diving into code or diagrams.

Leadership – Even in individual contributor roles, you are expected to influence your squad. Show that you can communicate technical constraints to non-technical stakeholders and that you take ownership of the quality and reliability of your deliverables.

Culture fit – SumUp values simplicity and ownership. Demonstrate that you are results-oriented, collaborative, and capable of working in a diverse, international environment where feedback is frequent and direct.

The SumUp interview process is designed to be thorough yet efficient, focusing on assessing your practical skills through real-world scenarios. You can expect a series of stages that typically begin with a recruiter screening, followed by deep-dive technical sessions that may include live coding or system design discussions. The process is highly collaborative, and you will likely meet with members of the engineering team you would be working with daily.

This timeline provides a high-level view of the stages you will encounter, from initial screening to final technical assessments. Use this to pace your preparation, ensuring you have enough time to brush up on both your system design fundamentals and your language-specific technical skills. Remember that the process is designed to be a two-way street; use the later stages to ask your interviewers about their team’s specific challenges and engineering culture.

System Design & Scalability

This area is critical for Backend Engineers at SumUp, as the platform must handle thousands of transactions per second. You are evaluated on your ability to design systems that are not only functional but also resilient, observable, and maintainable.

Be ready to go over:

• Distributed systems – Understanding consistency, availability, and partition tolerance (CAP theorem).
• Database design – Choosing the right storage engine for the right data access pattern.
• Microservices patterns – Service discovery, circuit breakers, and event-driven architectures.

Example scenarios:

• "How would you design a rate-limiting service for our API?"
• "Describe the architecture for a background job processing system."

Coding & Implementation

This area tests your ability to write production-ready, clean, and efficient code. You will be expected to demonstrate proficiency in writing idiomatic code, particularly in Golang.

Be ready to go over:

• Concurrency – Using goroutines and channels effectively.
• Error handling – Writing robust code that fails gracefully.
• Unit and Integration testing – Ensuring your code is reliable.

Example scenarios:

• "Implement a thread-safe cache in Golang."
• "Refactor this snippet to improve performance and readability."

As a Backend Engineer, your primary responsibility is to build and maintain the robust services that power SumUp’s financial products. You will work within a squad to define the technical requirements for new features, ensuring that the backend architecture is scalable and secure. You will be responsible for the entire lifecycle of your services, from initial design and development to deployment and ongoing monitoring.

Collaboration is central to your daily work. You will work closely with product managers to understand user needs, with frontend engineers to define APIs, and with site reliability engineers to ensure high availability. You will also participate in code reviews, contribute to technical documentation, and play an active role in improving the engineering practices within your team.

A strong candidate for this role possesses a mix of deep technical expertise and a pragmatic approach to software development.

• Must-have skills – Strong experience with Golang or a similar backend language, deep understanding of microservices architecture, experience with SQL and NoSQL databases, and proficiency in cloud-native technologies.
• Nice-to-have skills – Experience in the fintech or payments industry, familiarity with Kubernetes and CI/CD pipelines, and experience with high-concurrency systems.
• Experience level – Proficiency in software engineering principles is essential, typically demonstrated through several years of experience in backend development.

Q: How much time should I spend preparing? A: Most candidates spend 2–4 weeks preparing, depending on their familiarity with system design and Golang. Focus on refreshing your knowledge of distributed systems and practicing coding problems in your preferred language.

Q: What is the company culture like? A: SumUp is known for its fast-paced, collaborative, and ownership-driven culture. You will be expected to be proactive, take responsibility for your work, and contribute to a team environment that values direct feedback and continuous improvement.

Q: Will I need to know specific technologies? A: While general engineering principles are most important, experience with Golang is highly valued. If you are not an expert in Golang, be prepared to show your ability to learn it quickly by drawing parallels to other languages you know.

• Think out loud: When solving coding or design problems, explain your thought process clearly. Interviewers want to see how you approach problems, not just the final result.
• Ask clarifying questions: Never jump into a solution without confirming your understanding of the requirements and constraints.
• Connect to the business: Always try to link your technical decisions to the user or business impact.
• Be honest about trade-offs: There is no perfect system. Acknowledge the trade-offs in your design choices to show maturity.

The Backend Engineer role at SumUp offers a unique opportunity to work on high-impact financial infrastructure within a dynamic, global environment. By focusing on deep technical mastery, architectural scalability, and clear communication, you will be well-positioned to succeed in the interview process. Remember that SumUp values engineers who take ownership and approach challenges with a user-first mindset.

You can explore additional interview insights, practice questions, and preparation resources on Dataford. We encourage you to use this guide as a foundation for your preparation, tailoring your focus to the areas where you need the most growth. With focused, deliberate practice, you can demonstrate the expertise and cultural alignment that the team is looking for.

The provided compensation data reflects typical ranges for this role, which may vary based on your specific level of seniority, location, and the specific team you join. Use this as a reference to understand the market value for this position, keeping in mind that total compensation often includes base salary, benefits, and potentially other performance-based components.