SumUp Mobile Engineer interview questions & guide 2026

Our interview process is designed to evaluate your practical engineering skills and your ability to work within a collaborative, cross-functional team. The following categories represent the core pillars of our assessment, drawn from consistent patterns in our evaluation process.

Technical Proficiency and Domain Expertise

These questions focus on your daily bread-and-butter: writing, debugging, and architecting mobile solutions. We want to see how you think about platform-specific constraints and modern mobile development patterns.

• Review Kotlin or Swift code snippets and identify design issues or potential bugs.
• Explain the output and order of operations in asynchronous code.

Preparation at SumUp requires a balance of hands-on coding and clear, concise communication. You should be prepared to discuss not just how you solved a problem, but why you chose a specific approach over others.

Technical Competency – We expect you to be fluent in your primary language (Kotlin for Android or Swift for iOS). You should be comfortable refactoring existing code, discussing unit tests, and explaining how you ensure code quality.

Problem-Solving Approach – We evaluate how you structure your thoughts when faced with ambiguity. Whether it is a take-home challenge or a live coding session, explain your trade-offs clearly—especially regarding performance, maintainability, and user experience.

Team Alignment and Communication – We look for candidates who proactively collaborate with cross-functional partners. Be prepared to explain how you resolve technical disagreements and how you keep stakeholders informed throughout the development lifecycle.

Growth Mindset – We value engineers who are curious and open to feedback. During technical deep dives, demonstrate your ability to listen to suggestions and pivot your approach when presented with new information.

The SumUp interview process for a Mobile Engineer is designed to be thorough. It typically involves an initial screening, a technical assessment, and several rounds of deep-dive discussions with engineers and management. We aim to assess your technical depth, your ability to handle real-world engineering constraints, and your compatibility with our collaborative, merchant-first culture.

You should anticipate a process that moves from high-level discussions of your experience to granular reviews of your code and, finally, to behavioral assessments. While the process can be long, it is structured to ensure that we understand your full range of capabilities before making a decision. We prioritize transparency and encourage you to ask questions about our technical challenges and team dynamics throughout each stage.

This timeline provides a high-level view of the progression from initial screening to final team-fit discussions. Use this to pace your preparation, ensuring you have enough time to revisit core technical concepts before the live coding and technical review stages. Note that specific stages may vary slightly based on the team's immediate needs and the seniority level of the role.

Code Quality and Refactoring

We place a high premium on your ability to write clean, maintainable code. In interviews, we often provide existing snippets to see how you identify technical debt and improve readability.

Be ready to go over:

• Refactoring techniques: Identifying "code smells" and applying design patterns.
• Testing: How you integrate unit and UI tests to ensure stability.
• Platform specifics: Understanding the nuances of memory management and threading in your target OS.

Example questions or scenarios:

• "Here is a piece of legacy code; how would you refactor it to make it more testable?"
• "What is wrong with this implementation regarding thread safety?"

Cross-Functional Collaboration

As a Mobile Engineer, you are not working in a silo. We evaluate your ability to bridge the gap between technical constraints and product requirements.

Be ready to go over:

• Stakeholder management: How you handle conflicting requirements from PMs and designers.
• Conflict resolution: Providing concrete examples of how you have navigated disagreements with peers.
• Communication: Your ability to explain technical trade-offs to non-technical partners.

Example questions or scenarios:

• "How do you handle a situation where a product requirement is technically infeasible within the current sprint?"
• "Tell me about a time you had to persuade a stakeholder to prioritize technical debt."

As a Mobile Engineer at SumUp, your day-to-day will involve building features that directly impact our merchants. You will spend a significant portion of your time writing high-quality, testable code in Kotlin or Swift, ensuring that our apps remain performant under varying network and hardware conditions.

You will also be deeply involved in the architectural evolution of our applications. This includes modularizing codebases to improve build times, implementing new UI components using Compose or SwiftUI, and collaborating with backend teams to define robust API contracts. You will participate in code reviews, mentor team members, and occasionally lead technical investigations into production issues.

Collaboration is the backbone of your success. You will work in squads that include designers, product managers, and QA engineers. Your role is to act as a technical partner, offering insights early in the design phase to prevent bottlenecks and ensuring that the final output is both technically sound and delightful for our merchants to use.

A competitive candidate for a Mobile Engineer position at SumUp combines deep technical skill with a pragmatic, merchant-focused mindset.

• Technical Skills – Proficiency in Kotlin (Android) or Swift (iOS) is essential. You must have a strong grasp of MVVM/MVI architectures, unit testing frameworks, and modern UI toolkits like Jetpack Compose or SwiftUI. Experience with CI/CD pipelines and modularization is highly valued.
• Experience Level – We look for engineers who have worked in professional, collaborative environments. Experience with "offline-first" applications or payment systems is a major plus.
• Soft Skills – You must be a clear communicator who thrives in cross-functional teams. We value individuals who take ownership of features from inception to production and who can provide constructive feedback to peers.

Q: How long does the entire interview process usually take? A: The process typically spans three to five weeks, depending on team availability and the complexity of the role. We value your time and aim to keep communication open throughout.

Q: What is the best way to prepare for the technical assessment? A: Focus on practical application rather than theoretical algorithms. Review your understanding of clean architecture, dependency injection, and how to write effective unit tests in your primary language.

Q: Does SumUp value culture fit? A: Absolutely. We look for engineers who are collaborative, humble, and deeply invested in the success of our merchants. We want to work with people who treat their teammates with respect and are eager to learn.

Q: Can I expect feedback if I am not selected? A: We strive to provide timely updates to all candidates. While we aim to be as transparent as possible, please note that the depth of feedback can vary by stage.

• Own your narrative: When discussing past projects, be ready to explain the "why" behind your technical decisions, not just the "what."
• Focus on the merchant: Always frame your technical decisions through the lens of how they improve the user experience or business efficiency.
• Ask meaningful questions: Use the end of your interviews to ask about our engineering culture, how we handle technical debt, or how our teams are structured. It shows you are thinking critically about your future environment.
• Be prepared for ambiguity: In our team-fit or design sessions, we may present open-ended scenarios. Don't panic; clarify the requirements, state your assumptions, and walk us through your logic step-by-step.

The Mobile Engineer role at SumUp is a unique opportunity to shape the financial tools used by millions of small businesses. By focusing on your core technical strengths, clear communication, and a pragmatic approach to problem-solving, you will be well-positioned to succeed in our rigorous evaluation process. Preparation is your greatest advantage, so we encourage you to reflect on your past projects and practice articulating your technical trade-offs with confidence.

You can explore additional interview insights, practice questions, and preparation resources on Dataford to further sharpen your skills. We look forward to seeing the unique perspective and engineering expertise you can bring to our team.

The compensation data provided reflects the typical salary ranges and components for Mobile Engineer roles within our organization. Use these figures as a benchmark to understand the market value of your experience and the various components of a total rewards package, including base salary and potential benefits.