Senior Software Engineer, Online
First seen by Alion on Oct 6, 2026.
About the job
Flatpay has become one of the fastest-growing payment companies by helping merchants accept payments in-store. Now we're taking the next step.
Online is one of Flatpay's newest and most strategic engineering domains. We're building the products and platforms that enable merchants to accept payments online and grow their businesses in the digital economy. As a Senior Software Engineer, you'll play a key role in defining the technical direction of Flatpay's online platform and helping establish the technical and architectural foundations that will support the next phase of Flatpay's growth.
This is a unique opportunity to join at an early stage. While Flatpay already serves merchants at scale, our online platform is still in its early stages. You'll have the opportunity to help launch new solutions, shape how the platform evolves as adoption grows, and learn directly from customers along the way.
If you enjoy building products from the ground up, working close to customers, and seeing your work evolve from first launch to large-scale adoption, you'll have the opportunity to make a significant impact in a domain that will play an important role in Flatpay's future growth.
What you'll do
Design and build scalable systems that power online payments and commerce experiences
Lead feature and platform initiatives involving multiple engineers, driving delivery from discovery through production
Take ownership of features from design and implementation through deployment and maintenance
Drive architectural decisions and long-term technical improvements
Build APIs, services, and integrations that enable online payment experiences
Improve reliability, observability, performance, and security across the platform
Partner with engineers, product managers, and stakeholders to drive technical and product outcomes
Mentor engineers through coaching, code reviews, and knowledge sharing
Help establish engineering standards and best practices as the Online domain continues to grow
Who you are
7+ years of professional software engineering experience
Strong experience designing and operating distributed systems
Demonstrated ability to lead technical projects involving multiple engineers and influence architectural decisions
Experience building scalable backend platforms and APIs
Comfortable navigating ambiguity and helping shape new products and systems
Strong communication and collaboration skills
Experience within payments, fintech, e-commerce, SaaS, or high-scale transaction systems is a plus
You'll be working with technologies such as the following. We don't expect experience with every technology listed below. We're looking for engineers who can learn quickly and help us build great products.
Backend
Java, Spring Boot
MySQL
REST APIs & Event-Driven Architecture
Domain Driven Design
Docker, AWS
Frontend
TypeScript
React
TanStack Query
Jest
Playwright
i18n, feature flags
Platform & Delivery
GitHub Actions
CI/CD
AWS ECS
Observability & Monitoring
Why Flatpay?
As part of our team, you'll join 2,000+ passionate Flatpayers dedicated to shaping the future of payments.
You'll help build a strategic new business area from the ground up, working on products that directly connect merchants and consumers while shaping the future of online payments at Flatpay.
We offer an inclusive environment where engineers are trusted with ownership and encouraged to make an impact.
Our engineering teams work together from our Copenhagen office. We believe that close collaboration, quick feedback loops, and solving problems side-by-side help us build better products, move faster, and create a stronger engineering culture.
We also provide plenty of perks including free slush ice, an on-site gym, a fully equipped gamer room, and much more.
If you're ready to help build and scale the future of payments, we'd love to hear from you.
Perks and benefits
This job comes with several perks and benefits
Near public transit
Near public transit
Free office snacks
Free office snacks
Paid holiday
Paid holiday
Free coffee / tea
Free coffee / tea
Work life balance
Work life balance
Flexible working hours
Flexible working hours
See all 18 benefits
Working at
Flatpay
WHAT IS FLATPAY? At Flatpay, we believe that merchants deserve a payment solution that is easy to understand, affordable, and free from hidden fees. That's why we offer a straightforward pricing model with no setup fees for terminals, no subscription fees, and a flat rate for all card types. It's a breath of fresh air compared to the complicated and confusing pricing structures of our competitors. What sets Flatpay apart is our dedication. We continuously strive to stay ahead of the curve, adapting our solutions to meet our client's evolving needs. Ready to be part of something extraordinary? WHAT's THE CULTURE LIKE? Flatpay is a fast-moving, performance-driven environment where people are trusted to take ownership from day one. We value initiative, resilience, and a strong work ethic. Our teams are collaborative and supportive, but we also set clear expectations and hold ourselves accountable to results. As a growing business, things move quickly. That means you’ll have the opportunity to take on real responsibility early, contribute ideas, and see the impact of your work directly. It also means being comfortable with change, solving problems as they arise, and continuously improving how we operate. We’re best suited to people who are motivated by challenge, enjoy working towards clear goals, and want to develop in a commercial, high-energy environment. WHY CHOOSE FLATPAY? Flatpay offers the opportunity to take real ownership, develop valuable skills, and grow your career in a fast-moving, ambitious company where performance and initiative are recognised.