Senior Full Stack Developer (.Net)

Company Description

Hastee, a Zellis company, is an award-winning fintech start-up providing a market-leading financial well-being solution. Our platform allows workers to get paid flexibly at any time of the month, provides money management and budgeting support, and helps them save sustainably. We deliver this in a B2B2C model, selling our solution to major employers, who in turn offer the Hastee app as a corporate benefit to their staff.

Our revolutionary technology is designed to improve the productivity of the workforce and in turn, their organizations, and we are proud to have an NPS of 76 and 4.8/5 rating in the Apple Store and Google Play. Unsurprisingly, we’ve already won over 300 amazing clients, including McDonald’s, PayPal, and the NHS, and are now on a fantastic growth journey.
Hastee was founded with a socially driven mission and has offices in Barcelona and London. We are backed by some of the leading fintech investors and are playing a crucial role in supporting workers affected by the cost-of-living crisis.

Job Description

Responsibility:

• Design, develop, and maintain scalable and high-performing web applications using .NET (C#, ASP.NET Core) for the backend and React for the frontend.

• Develop and consume RESTful APIs and other backend services.

• Write clean, well-documented, and efficient code following best practices and coding standards.

• Collaborate closely with product managers, designers, and other engineers to understand requirements and translate them into technical solutions for web and potentially mobile applications.

• Build reusable and efficient React components and frontend architectures.

• Contribute to database design and optimization (e.g., SQL Server, PostgreSQL).

• Participate in code reviews to ensure code quality and knowledge sharing across the team.

• Troubleshoot, debug, and resolve software defects across the full stack (backend and frontend).

Qualifications

• Minimum of 5+ years of professional experience as a Full Stack Developer.

• Strong proficiency in C# and .NET Core/.NET 8.

• Solid understanding of web development principles, including RESTful APIs, HTTP, and security best practices.

• ​​Extensive experience with React and its core principles.

• Experience with HTML, CSS, and modern JavaScript (ES6+).

• Familiarity with database systems (e.g., SQL Server, PostgreSQL, MySQL) and ORM frameworks (e.g., Entity Framework Core).

• Strong communication skills and ability to collaborate in a remote-first environment.

• Good in English (Spanish is a plus)

Additional Information

Why Join Us:

• Flexible work environment (hybrid or fully remote in the Spain).

• Opportunity to work with cutting-edge technologies in a fast-growing fintech startup.

• Strong engineering culture with a focus on quality, scalability, and innovation.

• A supportive, diverse, and dynamic team that values growth and learning.

• Work on a product that makes a real social impact on financial well-being.