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