Altimi is a technology acceleration partner with impressive experience spanning over 20 years, specializing in the successful delivery of software development projects for international customers. We are based in Poland. Our main area of operation is the DACH region and Scandinavia, where we are known for providing top-notch software development services. Our primary focus are managed services for companies seeking to accelerate growth, solve complex tech problems, build MVP/POC and/or modify legacy infrastructures. The main area of competence include Product & Application Engineering, DevOps, Cloud Security & Managed Services and AI & Data Enablement.  Senior Backend Developer (C# / API / MSSQL) About ProjectThe project involves taking over the maintenance and development of an existing billing and usage-tracking platform used for automated invoicing based on collected consumption data from infrastructure systems.The scope includes technical ownership of the current solution, implementation of system adaptation due to changes in the external contract management platform, and development of a new integration to ensure full continuity of billing processes.The platform consists of a data ingestion layer, database logic, backend API and internal frontend interface. Data is collected from multiple enterprise sources, normalized, and processed for invoice calculations. The project requires maintaining high accuracy of financial output, and seamless migration to the new integration endpoint within a defined MVP.Role OverviewThe Senior Backend Developer is responsible for designing, developing, and optimizing backend services and APIs to support advanced integration models and business logic. This role focuses on high-performance, scalable solutions within the client’s API ecosystem, ensuring data integrity and operational efficiency.Responsibilities: Develop and adapt backend API (C#) and business logic (billing, status, mappings) Modify SQL logic (views, functions, performance improvements) Implement integration endpoints and data synchronisation Optimise data processing for large data volumes Participate in KT and technical discussions Requirements: 8+ years of experience in C# (.NET Core / ASP.NET) Strong understanding of MSSQL (stored procedures, indexing, performance tuning) Experience working with large-scale data processing  Nice to have Experience in system integrations, Azure React We Offer MultiSport card LuxMed medical package Allianz group insurance Value-based work culture Flexible working hours and remote work options