Senior Full Stack Developer - Fintech Startup

About our fintech startup

Berlin-based fintech company building next-generation payment infrastructure needs senior full stack developer with deep expertise in scalable systems and financial technology. We are disrupting traditional banking with modern API-first solutions serving enterprise clients across Europe.

Technical responsibilities

Build and maintain full stack features from database to user interface for our payment platform. Architect scalable backend services handling high transaction volumes with zero downtime requirements. Develop RESTful APIs consumed by web and mobile applications with strict performance SLAs. Implement complex business logic for payment processing, reconciliation, and fraud detection. Design and optimize database schemas for financial data with ACID compliance. Build responsive frontend interfaces using modern JavaScript frameworks. Integrate with third-party banking APIs, payment gateways, and KYC providers. Write comprehensive tests ensuring reliability for mission-critical financial operations. Participate in code reviews maintaining high engineering standards across the team. Debug production issues quickly minimizing impact on customers and transaction flow.

Required technical expertise (5+ years)

Backend development: Expert-level Node.js or Python building production-grade APIs at scale. Deep understanding of relational databases (PostgreSQL) including query optimization and indexing strategies. Experience with message queues (RabbitMQ, Kafka) for asynchronous processing. Knowledge of microservices architecture and distributed systems patterns. Understanding of security best practices for handling sensitive financial data.

Frontend development: Advanced React.js or Vue.js with state management (Redux, Vuex). TypeScript proficiency for type-safe application development. Responsive design implementation ensuring cross-browser compatibility. Experience with modern build tools (Webpack, Vite) and CI/CD pipelines.

DevOps and infrastructure: Docker containerization and Kubernetes orchestration experience. AWS or Google Cloud Platform services (Lambda, RDS, S3). Monitoring and logging tools (Datadog, Sentry) for production observability. Git workflow and branching strategies for team collaboration.

Fintech-specific requirements

Proven experience building payment systems, banking applications, or financial platforms. Understanding of PSD2, GDPR, and European financial regulations. Knowledge of double-entry bookkeeping and financial reconciliation processes. Experience with API security including OAuth 2.0, JWT, and encryption. Handling of money calculations with precision avoiding floating-point errors. Understanding of idempotency for financial transactions preventing duplicate charges.

What we need beyond technical skills

Senior-level problem-solving ability architecting solutions from scratch. Ownership mindset taking features from concept through deployment. Clear technical communication explaining complex systems to non-technical stakeholders. Code quality standards writing maintainable, well-documented code. Mentorship capability helping junior developers grow their skills. Proactive approach identifying technical debt and suggesting improvements.

Position details: Fully remote at $2500 monthly. Must work European business hours (CET/CEST timezone) for team collaboration. English fluency required for technical discussions and documentation. German language skills are a plus but not mandatory. This is a senior role with significant technical ownership and architectural influence. Your code handles real money for real businesses - reliability and security are paramount.