Senior Integration Engineer/Backend Engineer (.Net&AWS)

Our client is a leading European online car marketplace, connecting car buyers and sellers across the continent. The platform serves over 30 million monthly users and operates across 18 countries, making it one of the largest and most trusted digital marketplaces for vehicles in Europe. We are looking for Senior Integration Engineer to join an established client squad, working closely with its members and reporting to the squad's Tech Lead. You will contribute to two integration initiatives - Workday-to-Data-Lake and Marketplace-to-HubSpot — and are expected to work across both solutions, with sufficient overlap in skills to avoid dependency on a single consultant. You will not be solely responsible for the solutions: technical direction, architecture alignment, prioritisation, and delivery oversight remain with the client squad and its Tech Lead. This is a hands-on engineering role within a collaborative, established team that values knowledge sharing and clear documentation. Responsibilities: Design, build, and maintain .NET-based integration services and microservices supporting the Workday-to-Data-Lake and Marketplace-to-HubSpot initiatives. Develop, deploy, monitor, and operationally support cloud solutions on AWS, ensuring secure configuration throughout. Implement robust API integrations covering authentication, data contracts, pagination/batching, rate limits, retries, error handling, and idempotent processing. Build event-driven and asynchronous integration flows, including webhooks, scheduling, historical loads, and incremental data feeds.Ensure data quality and reconciliation across integration pipelines, with clear source-of-truth ownership and secure handling of financial and operational data. Partner with the squad's Tech Lead and team members to align with the existing reference architecture, priorities, and delivery plans. Produce clear technical documentation and actively share knowledge within the engineering team. Maintain skill overlap with the second integration engineer across both solutions to ensure delivery continuity. Requirements: 3+ years of experience in AWS/cloud and .NET Core development, ideally in an integration-focused engineering role. Proven experience building .NET-based integration services and microservices. Hands-on AWS/cloud experience across development, deployment, monitoring, secure configuration, and operational support. Strong API integration expertise: authentication, data contracts, pagination/batching, rate limits, retries, error handling, and idempotent processing. Solid grounding in event-driven and asynchronous integration patterns. Experience with data ingestion and integration pipelines, including historical loads, incremental feeds, scheduling, and webhooks. Track record of ensuring data quality, reconciliation, and secure handling of financial or operational data.Strong collaboration, documentation, and knowledge-sharing skills within an established engineering team; excellent verbal and written English skills. Nice to have: HubSpot API integration experience. Workday API or finance/ERP integration experience. Data Lake ingestion and structured data landing patterns. CRM and operational-workflow integrations. Experience extending or aligning with an existing reference architecture. We offer*: Flexible working format - remote, office-based or flexible A competitive salary and good compensation package Personalized career growth Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more) Active tech communities with regular knowledge sharing Education reimbursement Memorable anniversary presents Corporate events and team buildings Other location-specific benefits *not applicable for freelancers