Senior Software Engineer Backend – FinTech & Digital Assets

About Us Our client is an ambitious European FinTech company in the build-up stage, bridging the gap between traditional finance and blockchain technology. With the clear goal of establishing a secure and fully MiCA-compliant on-chain payment infrastructure for Europe's digital economy, a highly experienced team is building next-generation settlement solutions. This is an opportunity to actively shape the financial infrastructure of tomorrow. Responsibilities Infrastructure Ownership You will take full responsibility for the crypto custody and transaction infrastructure (based on Fireblocks) and transition it from an external agency into the company's internal core system. Backend Development You will develop production-ready features and scalable microservices within the Kotlin / Spring Boot backend environment. Event-Driven Architecture You will design and maintain RESTful APIs and event-driven workflows (Kafka-style), ensuring idempotency and fault tolerance. Security & Compliance You will implement secure authentication and authorization flows (OAuth/OIDC via Zitadel) and embed a "compliance-by-design" approach into the codebase to ensure successful audits. Requirements JVM Expertise 5–8 years of backend development experience. Strong focus on Kotlin. Strong Java experience is also acceptable. Tech Stack Experience Spring Boot. PostgreSQL. Kafka or similar event-streaming/messaging systems. FinTech & Regulatory Mindset Experience in regulated or ISO-certified financial environments, such as: ISO 27001 PCI-DSS You understand that auditability and traceability are core product features, not administrative burdens. Soft Skills Proactive and self-driven working style. Ability to explain technical concepts to non-technical stakeholders. Languages Fluent professional English (company language). Nice-to-Have Experience with crypto custody platforms, preferably Fireblocks. Interest or experience with: DeFi Blockchain concepts Smart contracts Ethereum Hardhat Cloud or security certifications: AWS ISTQB Similar certifications