Kotlin Backend Engineer - (Freelance/Service Agreement)

We are looking for a skilled Kotlin Backend Engineer for service agreement collaboration. B2B Sales Distribution team builds and operates the backend platform powering Flix's partner-facing ecosystem — including a self-management platform for partners, a back office portal for internal users, and an AI agentic bot supporting partner operations. The team is driving a significant modernization of its backend architecture and is working in an AI-native development environment. Scope of services • Independent delivery of backend services in Kotlin and Spring Boot, including design, development, and maintenance • Building and maintaining REST APIs used by internal and external partners • Contributing to architectural decisions and technical modernization initiatives as a senior topic driver • Improving observability, performance, and reliability of backend systems using DataDog • Supporting CI/CD pipelines and cloud infrastructure on AWS and Kubernetes • Working within an AI-native development environment, including CI-integrated code review automation and an internal Claude Code plugin marketplace covering Kotlin/Spring Boot conventions, architectural patterns, testing practices, and database guidelines • Sharing Kotlin expertise and best practices with existing engineers on the Flix team who are transitioning from other languages, through code review, pairing, and technical guidance Relevant expertise • 4+ years of software engineering experience, primarily backend development with a JVM language, including some commercial experience with Kotlin • Hands-on Spring Boot experience • Experience building and maintaining REST APIs and distributed systems • Solid SQL knowledge and relational database design, including MySQL and PostgreSQL • Sound software engineering fundamentals and clean code practices • Clear written and spoken English communication skills • Preferred experience with: AWS, Kubernetes, GitLab CI/CD, Kafka, Terraform, LLM integrations, RAG systems, AI product development, or legacy system migration experience Collaboration model • Cooperation based on a service agreement with independent delivery of agreed services and invoicing