Senior Full Stack Engineer - Sidekick

Senior Full Stack Engineer - Sidekick

The Sidekick team builds and owns the progressive web app that Sum Ups field sales agents rely on every day, a tool that brings together everything a seller needs in one place: creating offers on the go, signing up new merchants, managing hardware sales, and tracking commissions in real time. It's one of our most impactful internal products, sitting at the heart of a primary revenue driver for the business.

As our Senior Full Stack Engineer, you'll take genuine ownership of features end-to-end, from scoping through to production, working closely with product, engaging directly with sales stakeholders, and having a real say in what gets built and why. If you want autonomy, meaningful scope, and work that directly enables the people driving Sum Up's growth, this is the role.

What you'll do

• Build and maintain features across the full stack of our progressive web app, spanning the field sales experience, back office tooling for sales agents, and emerging LLM-powered support tooling, owning work from scoping through to production
• Participate actively in product discovery, joining user research sessions, reviewing usage data, and contributing to prioritisation discussions alongside product
• Work directly with sales stakeholders to understand their needs, distinguish between what's requested and what's actually needed, and propose solutions with clear trade-offs
• Contribute to raising engineering standards across the team, through documentation, code quality, and proactive process improvements
• Integrate with external systems such as Salesforce where required, and help shape how data flows across domains to create a consistent experience for field sellers

You'll be great for this role if

• Strong, proven experience with React and Type Script, building scalable, maintainable applications in a production environment.
• Hands-on experience with a full-stack framework, Next.js, Remix, Nuxt, or similar, with a clear track record of shipping real-world features end-to-end.
• Experience building or consuming RESTful APIs and working within complex micro service systems.
• Comfortable as a Kubernetes user, with exposure to working in cloud-native, distributed environments.
• Experience working in a product-led or dual-track agile team alongside our product team, contributing to product decisions, not just technical ones.
• A natural tendency to reach out to stakeholders, ask the right questions, and bring genuine empathy to the end user's experience.
• Comfortable showcasing and demoing work, and always looking for ways to simplify or automate where it makes sense.

Why you should join Sum Up:

• 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 Sum Up's future success
• A dedicated annual L&D budget of €2000 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 Sum Up team

About Sum Up

Be empowered to do more that matters.

At Sum Up, 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 Sum Up 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 Sum Uppers from over 90 nationalities, united by global…