We’re seeking a Senior Back-end Developer who will be a primary builder of this platform. You will implement the robust, scalable, and secure microservices that form the core of our multi-tenant architecture. You will adhere to the OpenAPI contract, ensuring every service you build, from real-time billing and reporting to the campaign approval flow, is reliable, high-performing, and perfectly aligned with the detailed business logic.Immerse yourself in a high-load AdTech environment, collaborating on real-time integrations with ad servers, CRMs, and payment providers. This role involves modernizing the existing architecture, refactoring legacy monolithic components into cloud-native microservices running on AWS, and designing the secure API infrastructure necessary for future integrations, including advanced machine learning and AI models. Your technical expertise will directly empower thousands of global advertisers.CustomerOur Customer is a Swedish AdTech company that transforms the way publishers and advertisers interact. They provide state-of-the-art self-serve advertising platforms that enable seamless, direct transactions between advertisers and some of the world’s largest publishers. Their mission is to make advertising more accessible, automated, and efficient through innovative technology. Together, we serve globally recognized clients, including TripAdvisor, Bloomberg, The Washington Post, Opera, Dow Jones, etc.ProjectWe are building a white-label, self-serve advertising platform that is widely used by international media companies and publishers. The platform integrates with ad servers, CRMs, and payment systems, providing a unified interface for managing advertising campaigns. This system handles high volumes of real-time data and transactions, requiring exceptional performance and stability.Responsibilities Implement microservices (billing, reporting, approval) based directly on the OpenAPI specification and BRD logic Write clean, efficient code with a primary focus on strict multi-tenant data separation, authorization, and security Proactively refactor legacy monolithic code into cloud-native microservices, working closely with the Platform Architect Build the secure API infrastructure required to integrate AI model inference into core platform workflows

Develop highly testable code (unit, integration) to support the CI/CD pipeline and automated documentation generation

Requirements At least 7 years of hands-on Back-end development experience Proven experience with OpenAPI/Swagger-defined REST APIs Extensive experience designing, developing, and deploying containerized microservices (e.g., using Java, Node.js) Experience with relational and NoSQL databases optimized for multi-tenant SaaS applications Deep experience with monitoring, distributed tracing, and secure credential management in AWS environments At least an Upper-Intermediate level of English  Would be a plus Experience with Go (Golang) for high-performance services

Knowledge of building services for high-volume AdTech or FinTech platforms

Personal Profile Independent and proactive problem-solver Strong focus on writing clean, secure, and maintainable code Comfortable working in distributed, international teams