Senior Backend Engineer (Kotlin + GCP Required) [Freelancer for a Germany-based Startup]

About KothonTechKothonTech GmbH is a German tech talent platform that connects high-performing software engineers from Tunisia with innovative companies in Germany and across Europe. We collaborate with companies that build modern, scalable products and value quality engineering. We are currently looking for a Senior Backend Engineer (Kotlin + GCP Required) to join impactful client projects.Key ResponsibilitiesRebuild a Subscription Engine — Lead the development of a new, custom subscription solution.Backend Development in Kotlin (GCP) — Design and implement secure and scalable backend services on Google Cloud Platform.API Design & Integration — Build clear and maintainable APIs to power mobile applications and internal systems.(Note: The primary focus is backend logic and engine architecture, not front-end-heavy work.)B2B Product Enablement - Develop and enhance subscription features that support enterprise and business customers.Data Modeling & Storage — Create efficient data models and database schemas for subscription and billing workflows.Payment Gateway Integration — Implement integrations with multiple payment providers for seamless and reliable transaction processing.Testing & QA — Ensure reliability through unit, integration, and end-to-end tests.DevOps Collaboration — Contribute to CI/CD setup and deployment pipelines on GCP.Architecture Partnership — Work closely with the Head of System Architecture on system design and technical decision-making.Required QualificationsBachelor’s degree in Computer Science or a related field, or equivalent professional experience5+ years of experience as a Full Stack or Backend-focused Software EngineerStrong experience with Kotlin and React (or a willingness to become advanced in Kotlin quickly)Experience building and consuming APIs following domain-driven design principlesHands-on experience with event-driven architectures (e.g., GCP Pub/Sub or similar systems)Proficiency with Google Cloud Platform services and workflowsStrong debugging, problem-solving, and performance optimization skillsExperience writing and maintaining automated testsProven track record of shipping products and features in fast-paced environments.Self-efficacy & ownership: you manage workstreams and responsibilities effectively and proactively.Comfortable in a startup environment: you see uncertainty as an opportunity and enjoy experimenting.You communicate clearly in English — both in writing and speaking — with clients and your team.What We Offer2–3× The average Tunisian compensation – We value top talent and reward it accordingly.Remote work & flexible hours – Work from anywhere and set a schedule that suits your lifestyle.Exciting, modern projects – Collaborate with leading European tech companies on diverse and innovative projects.Developer-first culture – We prioritize learning, autonomy, and technical excellence.Flat hierarchy & long-term collaboration – Enjoy a supportive work environment with growth and stability.