Backend Software Engineer - Connect SDK

Hey there!👋

At Fourthline, our mission is to fight financial crime. We help protect the global financial system by verifying millions of identities for banks, neobanks, online brokers, crypto exchanges, or insurers like N26, Trade Republic, flatexDEGIRO, Nationale Nederlanden, Qonto, Shine, Solarisbank, and more.

Having started our journey in January 2018 only, we're incredibly proud to count around 250 employees between our Amsterdam and Barcelona offices with over 50 nationalities.

Join our Connect SDK team and power the solutions that business partners rely on. We're looking for a Backend Developer to work on the server-side infrastructure supporting our SDKs for Android, iOS, and Web platforms.
The Connect SDK team is cross-functional, taking ownership of Mobile, Web, and backend platforms. You'll collaborate closely with our SDK developers across all platforms to build robust backend services that enable seamless client integrations.   Why would you want to work here?

• Work with cutting-edge technology that supports millions of identity verifications
• Collaborate within a high-performing, cross-functional development team
• Clear career growth and learning opportunities in the FinTech space
• Freedom to make architectural choices and technical decisions
• Visibility and impact—your hard work, input and contributions will be used by consumers and customers
• Working in an agile environment, we deliver value through weekly releases

What you will do:

• Design and develop backend services that power our multi-platform SDKs
• Build and maintain APIs that support Android, iOS, and Web SDK functionality
• Implement secure, scalable microservices for identity verification workflows
• Collaborate with SDK developers across mobile and web platforms to ensure seamless integration
• Use data-driven development to optimize performance and reliability
• Maintain high security standards for sensitive financial data processing
• Contribute to architectural decisions that impact the entire SDK ecosystem

What you'll have:

• Minimum 3 years software development experience in one or more general-purpose programming languages
• Good knowledge of .NET 5-8, or .NET Core 3.x
• Proficiency in C# (version 10 or later)
• Familiarity with ORMs (EF Core) and knowledge of Linq
• Experience implementing REST APIs using .NET Web API
• Commitment to Code Quality: Adherence to healthy coding practices
• Experience with Git and CI/CD in Azure DevOps
• Experience with cloud providers such as AWS and Azure
• Ability to work on-site at our fantastic office in Barcelona at least 3 days a week as per our Hybrid Working Policy
• Language skills: English full professional proficiency

What would be nice to see:

• Experience working with frontend teams (mobile or web)
• Experience with EKS and Terraform is highly valued
• Experience with MSTest/NUnit are a plus

Our Stack
.NET 8-X – Our cloud-based microservices architecture includes REST APIs, Docker, Message Queues (RabbitMQ), RDBMS (PostgreSQL), Wolverine, Marten (Doc + Event stores), and much more!

At Fourthline, we believe diversity enriches our culture and inspires you to do your best work. We value your unique talents and perspectives, welcoming them into a safe and inclusive working environment, to ultimately deliver the best products to our customers and society. You're welcome here. Fourthline is for everyone. 

Our hiring process is designed to be equal, fair, and transparent. We welcome people from all backgrounds, ethnicities, genders, sexual orientations, ages, abilities, religions, and experiences in life. If you're excited about this role, but your experience does not align perfectly with every qualification in the job description, we encourage you to apply anyways. You may just be the right candidate for this or other roles.