? Senior Software Engineer – Backend | B2B SaaS | Barcelona

Would you like to join a fast-growing B2B SaaS company, building products that help businesses manage their HR, finance, payroll, expenses and IT processes?

We are looking for a Senior Software Engineer to join an engineering team responsible for building and evolving critical internal applications supporting sales, billing and financial operations.

We are not looking for someone specialized in a specific technology. We are looking for an engineer with a strong product mindset, capable of understanding complex problems, making architectural decisions and owning solutions end-to-end, from design to production.

?️ What will you do?

- Design and evolve the backend architecture of critical applications supporting sales, billing and financial operations.
- Build robust, scalable and resilient systems, with a strong focus on availability, performance, security and data integrity.
- Design reliable backend APIs and workflows capable of handling critical financial processes.
- Work with third-party integrations and payment platforms, as well as other external services.
- Own the full product lifecycle: problem definition, architecture, development, testing, deployment and production evolution.
- Work closely with Product, Design and other Engineering teams to turn business needs into effective technical solutions.
- Incorporate AI tools into your development workflow, using them to accelerate design, implementation, testing and problem-solving.
- Contribute to improving the team's engineering practices through code reviews, CI/CD, continuous deployment and collaborative specification definition.

? What are we looking for?




- 5+ years of professional experience as a Backend Engineer or Software Engineer.
- Experience building and maintaining production-grade APIs and backend systems.
- Strong knowledge of databases, Docker and cloud architectures.
- Ability to work across different languages and technologies and choose the right solution for each problem.
- Solid understanding of concepts such as concurrency, data integrity, fault tolerance, observability and system monitoring.
- A strong Product-First mindset: you understand not only how to build a solution, but also the problem it solves and its impact on the business.
- Experience working with cross-functional teams and Agile methodologies.
- Genuine interest in using AI as a regular part of the software development process.
- Good level of English, as you will work in an international environment.

⭐ Nice to have
- Experience in fintech, payments, billing or financial products.
- Experience integrating platforms such as Stripe, Adyen or other financial service providers.
- Experience building AI agents or LLM-powered applications.
- Experience with distributed systems and high-scale cloud architectures.

? What we offer? Barcelona

? Hybrid model: 4 days in the office + 1 day remote

? Salary: €60,500 – €86,250 gross/year, depending on experience and level

? Permanent contract

? International environment and B2B SaaS product

? AI-first culture applied to product development

If you are a Senior Software Engineer who enjoys understanding the problem, taking ownership and building systems that make it into production, this could be a great opportunity for you.

? Interested? Apply directly to the position.

📌 Senior Software Engineer (Barcelona)
🏢 HACK A BOSS
📍 Barcelona