Senior Backend Developer (C# & SQL)

A generalist recruitment company with specialised divisions acquiring the markets leading talent in engineering, renewable energy, manufacturing, FMCG manufacturing, finance, insurance, production, construction and mining. Are you an experienced Senior Backend Developer with a passion for designing scalable backend platforms, building robust integrations, and delivering high-performance enterprise solutions? Our client is seeking a Senior Backend Developer (C# & SQL) to design and build the backend platform foundation, including the business rules engine, integrations with multiple external systems, and core data models. This role is responsible for ensuring transactional consistency, data integrity, API design, and close collaboration with DevOps and QA teams to deliver secure and reliable backend solutions. The successful candidate will thrive in complex enterprise environments, working across development, support, and operational responsibilities while contributing to architectural decisions and mentoring fellow developers. Key Responsibilities Backend Development & Architecture Design and implement the business rules engine, including configuration storage, rule evaluation, and rule versioning. Design the backend for the rules engine administration interface, including rule management, audit trails, and approval workflows. Design document processing API integrations as an abstraction layer for future provider changes. Implement document validation and processing integrations. Design data models for multiple functional instruction types. Implement instruction payload constructors for downstream systems. Design region-specific routing logic for instructions. Design and implement immutable audit trails and event logging. Build integrations with multiple external systems. Implement transactional consistency across submission workflows. Lead backend architecture decisions and participate in solution architecture design. Mentor the development team on integration patterns and security best practices. Minimum Requirements Qualifications Bachelor's Degree or Diploma in Computer Science, Information Technology, Software Engineering, or a related field. Relevant cloud or software engineering certifications will be advantageous. AWS certifications will be beneficial. Experience & Technical Skills Minimum 8+ years' experience in C# backend development. Minimum 3+ years' experience working with SQL Server. Expert knowledge of C#, including ASP.NET Core, LINQ, async/await, and dependency injection. Expert SQL Server experience, including schema design, indexing, query optimisation, and transaction management. Experience with NoSQL or document store technologies. Strong experience designing and implementing RESTful APIs. Experience with API integration patterns, including retry logic, circuit breakers, and timeouts. Strong understanding of transaction processing and ACID compliance. Experience designing audit trails and event logging solutions. Experience with AWS RDS and cloud database services. Strong understanding of security best practices, including encryption, secrets management, and input validation. Experience using Git and CI/CD integration. Experience documenting APIs using Swagger/OpenAPI. Key Competencies Ability to work within complex enterprise environments. Strong debugging and root-cause analysis capability. Ability to learn and navigate custom frameworks and business logic. Effective communication and stakeholder collaboration. Ability to balance support, maintenance, and new development activities. Strong ownership mindset and operational accountability. Delivery Outputs Business rules engine with administration backend. Document processing integration abstraction layer. Data models for functional instruction types. Region-specific routing logic. Immutable audit trail and event logging system. Integrations with multiple external systems. API documentation and integration guides. Database schema documentation and migration scripts. What's on Offer Initial 6-month contract with the possibility of extension to 8 months or longer, depending on the project phase and business requirements. Opportunity to design and build enterprise-scale backend platforms and integrations. Work with modern backend technologies, cloud platforms, and secure API architectures. Play a key role in the delivery of complex enterprise solutions. Immediate start available, with preference given to candidates who can start immediately.