Senior Full Stack .NET Engineer (AI)

ImpacT Hire is supporting one of our clients – an established international payment technology company developing high-performance payment and acquiring solutions used by businesses worldwide.
We are looking for a Senior Software Engineer (AI) to join the engineering team responsible for the core backend systems behind the payment platform. This is a hands-on engineering role with a strong focus on C#/.NET, SQL Server, highly concurrent systems, and software architecture, combined with an important understanding of modern AI agent orchestration.
This is not a traditional Machine Learning role. We are looking for a strong software engineer who understands how AI agents execute tasks, manage state, interact with external tools, and orchestrate workflows, and who can design reliable backend systems that integrate effectively with these emerging AI architectures.

Responsibilities:
➢ Design, develop, and maintain core backend applications supporting a high-volume payment platform;
➢ Build high-quality, maintainable software using C# .NET Framework, while contributing to the transition towards .NET Core;
➢ Design backend services with clear and deterministic interfaces that can be effectively used within AI-driven and agentic workflows;
➢ Develop and optimize SQL Server stored procedures for highly concurrent and multithreaded production environments;
➢ Apply strong software design principles, patterns, and flow-based processing approaches to complex backend systems;
➢ Collaborate with Product, Engineering, QA, and other stakeholders to translate business requirements into robust technical solutions;
➢ Write automated unit tests and apply TDD and BDD principles to maintain strong engineering quality;
➢ Participate in code reviews and contribute to engineering standards and best practices;
➢ Contribute to the evolution of the platform architecture as it increasingly interacts with AI agents and orchestration layers;
➢ Participate actively in Agile ceremonies, including sprint planning, retrospectives, and daily stand-ups;
➢ Stay up to date with emerging engineering and AI technologies, particularly around the integration of enterprise software with agentic AI ecosystems.

Requirements:
➢ 4+ years of professional experience in software development with C# and .NET Framework and/or .NET Core;
➢ Strong hands-on experience with SQL Server, including stored procedures and database-intensive backend applications;
➢ Experience designing and developing backend systems operating in highly concurrent and/or multithreaded environments;
➢ Strong understanding of software design patterns and flow-based processing;
➢ Solid conceptual understanding of AI agent orchestration, including state management, agent loops, task execution, and tool-calling boundaries;
➢ Understanding of how backend services and APIs should be structured to serve as reliable, deterministic tools within AI agent workflows;
➢ Strong understanding of TDD and BDD principles and experience with relevant testing frameworks;
➢ Experience with Git and established branching workflows such as Gitflow;
➢ Strong analytical and problem-solving skills;
➢ Excellent communication and collaboration skills;
➢ Bachelor’s degree in Computer Science or another relevant technical field.

Nice to Have:
➢ Experience with SpecFlow or similar BDD tooling;
➢ Previous experience within online payments, FinTech, banking, or financial systems;
➢ Experience working with enterprise-scale, multi-server and highly multithreaded systems;
➢ Practical exposure to AI agents, agentic workflows, or AI-enabled enterprise applications;
➢ Experience designing APIs or services intended to be consumed by automated tools or orchestration layers.

What They Offer:
➢ Flexible remote or hybrid working model;
➢ Full-time, permanent employment;
➢ Opportunity to combine traditional backend engineering with emerging AI and agentic architecture concepts;
➢ Professional development and career growth opportunities;
➢ Collaborative international culture and cross-functional engineering environment.

If you are an experienced C#/.NET engineer who enjoys solving complex backend challenges and wants to work at the intersection of enterprise software, payment technology, and AI agent orchestration, this role offers the opportunity to apply strong software engineering fundamentals while helping shape how established systems evolve for the next generation of AI-driven workflows.