Senior Java Developer

Are you ready to take ownership of mission-critical backend systems in a high-load, transaction-heavy environment? We are looking for a Senior Java Developer to join our Payments Domain team in Warsaw. This is a hybrid role with 3 days per week in the office, giving you the perfect balance between collaboration and flexibility. At Sigma Software, we value engineering excellence, multicultural teamwork, and delivering secure, high-performance solutions. Why join us? You’ll work on a platform processing millions of transactions daily, contribute to architectural decisions, and be part of a company where innovation and ownership are encouraged. CUSTOMER Our customer is a well-established international company in the iGaming industry, known for its engineering-driven culture and multicultural team distributed across multiple countries. Operating multiple brands across various markets, the company delivers secure, high-performance digital platforms recognized for reliability and scalability. PROJECT You will be part of the Payments Domain team, responsible for developing and maintaining a large-scale payments platform built on modern microservices architecture. The platform processes millions of secure transactions daily, supporting multiple brands and geographies. The work focuses on scalability, reliability, and performance in a high-load environment, covering everything from integration with payment providers to transaction monitoring and compliance. Design, develop, and maintain backend services for the payments platform using Java and Spring Boot Ensure high availability, scalability, and performance of transaction processing systems Collaborate with cross-functional teams to define technical requirements and deliver solutions end-to-end Implement integrations with payment service providers and internal systems Participate in architectural discussions and contribute to system evolution in a microservices environment Monitor, troubleshoot, and optimize services in production Ensure compliance with security, regulatory, and operational standards Drive continuous improvement in code quality, testing, and deployment practices 5+ years of commercial experience with Java and Spring Boot Strong experience with MySQL and Kafka Proven track record working with microservices architecture in high-traffic, high-load systems Experience developing high-performance backend solutions for transaction-heavy platforms Ownership mindset with ability to deliver services end-to-end Excellent communication skills in English (C1 level), both written and verbal Experience with Kotlin