Senior Java Developer

Company Description 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. Job Description Design, develop, and maintain backend services for the payments platform using Java and Spring BootEnsure high availability, scalability, and performance of transaction processing systemsCollaborate with cross-functional teams to define technical requirements and deliver solutions end-to-endImplement integrations with payment service providers and internal systemsParticipate in architectural discussions and contribute to system evolution in a microservices environmentMonitor, troubleshoot, and optimize services in productionEnsure compliance with security, regulatory, and operational standardsDrive continuous improvement in code quality, testing, and deployment practices Qualifications 5+ years of commercial experience with Java and Spring BootStrong experience with MySQL and KafkaProven track record working with microservices architecture in high-traffic, high-load systemsExperience developing high-performance backend solutions for transaction-heavy platformsOwnership mindset with ability to deliver services end-to-endExcellent communication skills in English (C1 level), both written and verbalExperience with Kotlin