Senior Backend Software Engineer

At Scalapay, we’re shaping a culture with high standards, independent and critical thought, innovation, ownership, and continuous learning. We operate in a fast-moving, tech-driven environment, and we’re looking for people who thrive in change, think boldly, and take initiative. If you’re ready to put your potential to the test in a hiring process designed to spotlight exceptional talent, this is your chance to stand out and grow with one of Europe’s most ambitious fintech teams. #MakeItHappen #PlayAsATeam #StayCurious #FocusOnCustomer. The Mission Scalapay is an AI-first international fintech. We're looking for a Backend Software Engineer with banking platform experience to join our Consumer Banking team. You'll design and deliver high-performance, secure and scalable APIs that power our customer experience. You'll work spec-first: you define what good looks like, and AI coding agents help you build it faster without lowering the bar on quality, security or compliance.

Key Responsibilities
* Write clear specifications and technical designs that AI coding agents (e.g. Claude Code) implement from, then direct, review and test their output;
* Take full ownership of AI-generated code, making sure it meets our standards for security, performance and PCI DSS compliance before it ships;
* Use AI across the whole development lifecycle: test generation, code review, documentation, debugging and incident analysis;
* Help shape the team's AI tooling, shared context, prompts and guardrails so that development becomes more automated over time. API Development & Integration
* Design, build and maintain high-quality REST APIs using NestJS and TypeScript;
* Meet performance targets of under 200ms response time through caching, query optimisation, payload compression, rate limiting, pagination and filtering;
* Integrate with external services and banking partners, keeping the platform resilient to third-party failures.
* Build scalable, maintainable microservices using dependency injection, modular design and clean code principles;
* Develop event-driven systems and real-time features. Security & Compliance
* Implement authentication and authorisation (JWT, OAuth2, MFA) and API security measures (TLS, API key management, request signing);
* Apply secure coding practices, including input validation and protection against SQL injection and XSS;
* Ensure PCI DSS compliance and encryption of sensitive data at rest and in transit. Data & Infrastructure
* Design efficient MySQL/PostgreSQL schemas, manage migrations and optimise queries and indexing;
* Deploy on AWS with Docker, EKS, and CI/CD pipelines, working with DevOps on infrastructure requirements;
* Monitor system performance through logging, tracing and alerting. Required Qualifications
* 5+ years of backend development experience, including banking platforms, system integrations and ledgers
* 3+ years with NestJS and TypeScript, or comparable frameworks and languages
* Proven AI spec-driven development: you've shipped production software by specifying, directing and validating the work of AI coding agents
* Strong MySQL and/or PostgreSQL

skills:
schema design, query optimisation and indexing
* Deep knowledge of REST API design, plus GraphQL experience (code-first and schema-first)
* Track record of finding and fixing API performance bottlenecks, including caching (Redis, Memcached, HTTP caching)
* Strong API security background: authentication, authorisation, encryption, security testing and vulnerability assessment
* Experience with AWS (EC2, RDS, Lambda, API Gateway, CloudWatch) or a comparable cloud platform
* Solid testing practice (Jest, unit and integration testing), Git workflows and agile delivery What We're Looking For
* Banking platform experience. You’ve built or worked on banking systems, including system integrations and ledgers.
* An AI-first builder. You can show us AI projects that demonstrate your spec-driven way of working, and you have good judgement about when to trust AI output and when to challenge it.
* An owner. You think about performance, scalability and security by default, not as an afterthought.
* A collaborator. You're comfortable with code reviews and enjoy sharing what you learn, including the AI workflows that work for you.
* A continuous learner. You keep up with backend, security and AI-assisted engineering practices. Why Join Scalapay
* Attractive packages based on skills and experience, the salary band we have for this position is of EUR 65'000
- 80'000 (Gross Annual Salary);
* An international fintech with an AI-first approach, raising the bar daily on how we build software and solve complex problems
* Work alongside industry tech leaders focused on exceptional user experiences
* Personalised support to grow your career and take ownership of the products you deliver
* Modern technology and the freedom to bring your own flair Recruitment Process:
* A quick chat with one of our Talent Acquisition team members
* The first interview wi