Golang Developer (f/m/x)

We are looking for a Senior Golang Developer to join Sii and work on a large-scale backend system delivered in cooperation with a global organization operating in the US telecommunications market. The project focuses on building and evolving a critical platform that manages registration, verification, and the lifecycle of toll-free numbers used in SMS/MMS campaigns by business customers. You will contribute to a mature, event-driven system with strong domain logic, multiple external integrations, and real business impact. At Sii, we value long-term cooperation, stability, and continuous growth, offering access to mentoring, knowledge sharing, and further development opportunities across multiple projects. Apply now and let us match you with this or other suitable projects at Sii! Your tasks • Design, develop, and maintain backend services and REST APIs supporting customer-facing and administrative systems • Implement and evolve domain and service layers handling registration workflows, reviews, and lifecycle management • Integrate with external systems using synchronous APIs and asynchronous event processing • Work with PostgreSQL databases, including schema migrations and performance-oriented queries • Contribute to system reliability, scalability, and code quality in a distributed, event-driven architecture Requirements • At least 5 years of professional experience as a backend or software developer, including Golang • Strong knowledge of building HTTP APIs and backend services in distributed systems • Experience with relational databases, particularly PostgreSQL, and data migrations • Familiarity with event-driven architectures and asynchronous processing (e.g., Kafka) • English proficiency at B2 level or higher, enabling effective communication in an international environment • Residing in Poland required