Senior Software NET Engineer B2B

Reply Polska Sp. z o.o.; Katowice; Hybrid; PLN 180,000 - 240,000; Full time

Job summary

Nexi Digital is seeking a Senior Software Engineer to drive the modernization of a payment platform by migrating a large ASP.NET WebForms/MVC monolith from .NET Framework 4.x to .NET 8, updating the data layer and integrations in an on-premise environment.

You will apply SOLID and clean-architecture principles, mentor the team, and leverage AI-assisted tools to accelerate analysis, refactoring and test generation in a hybrid work setup.

Qualifications

• University degree in computer science or comparable field.
• 6+ years of commercial software development experience.
• Experience with C# and .NET across generations (Framework 4.x to .NET 8).
• Experience with migrating legacy applications (re-platforming, incremental refactoring).
• Knowledge of SOLID principles and clean architecture.
• Experience with SQL Server and data-layer refactoring.
• Experience with AI-assisted development tools (e.g., GitHub Copilot).
• Experience with automated unit and integration testing.
• Fluency in Polish and good English communication.

Responsibilities

• Migrate a large ASP.NET WebForms/MVC monolith from .NET Framework 4.x to .NET 8.
• Refactor to SOLID and clean architecture within the migration scope.
• Modernize SQL Server data layer and system integrations.
• Leverage AI-assisted tools to accelerate analysis, refactoring and test generation.
• Build automated test coverage (unit and integration).
• Collaborate with teams and stakeholders on scope and sequencing.
• Mentor less experienced developers and share modernization know-how.

Skills

C# / .NET

Legacy modernization

SOLID / clean architecture

SQL Server / data layer

AI-assisted development

Automated testing

Polish & English

Education

Computer science degree

Job description

Responsibilities

As a Senior Software Engineer at Nexi Digital, you will drive the modernization of an established, business-critical payment platform — migrating a large ASP .NET (WebForms/MVC) monolith from .NET Framework 4.x to .NET 8, together with its database layer and system integrations, in an on-premise environment. You will combine deep .NET craftsmanship with modern, AI-assisted ways of working to make the migration faster and safer. Analyzing the legacy codebase and shaping an incremental, low-risk migration path (module by module, no big-bang rewrites) Designing and implementing the migration of application components from .NET Framework 4.x / ASP .NET(WebForms, MVC) to .NET 8 / ASP .NET Core Refactoring the code towards SOLID principles and clean architecture as part of the migration, not as a separate project Modernizing the Microsoft SQL Server data layer and the platform's integrations with surrounding systems Using AI-assisted development tools (e.g. GitHub Copilot and LLM-based tooling) to accelerate legacy code analysis, refactoring and test generation — and helping the team adopt these practices responsibly Building the automated test coverage (unit, integration) that makes the migration verifiable at every step Collaborating closely with the development teams and stakeholders on scope, sequencing and technical decisions Mentoring less experienced developers and sharing modernization know-how across the team.

Qualifications

• Successfully completed university degree in computer science or a comparable field of study
• 6+ years of commercial software development experience
• Extensive experience with C# and .NET across generations — both .NET Framework 4.x (ASP .NET WebForms/MVC) and modern .NET (6/8) with ASP .NET Core
• Hands-on experience with modernizing or migrating legacy applications (re-platforming, incremental refactoring, strangler-fig-style approaches)
• Strong knowledge of software design principles and patterns, including SOLID and clean architecture
• Solid experience with Microsoft SQL Server and data-layer refactoring
• Practical experience with AI-assisted development (e.g. GitHub Copilot or similar LLM-based tools) as part of your daily engineering workflow
• Experience with automated unit and integration testing
• Fluency in Polish and very good communication in English

Availability to work in a hybrid mode. Remote workers, we invite to the office once every month

About Nexi Digital

Nexi is Europe's PayTech company operating in high-growth, attractive European markets and technologically advanced countries. Listed on Borsa Italiana's MTA, Nexi has the scale, geographic reach and abilities to drive the transition to a cashless Europe. With its portfolio of innovative products, e-commerce expertise and industry-specific solutions, Nexi provides flexible support for the digital economy and the entire payment ecosystem globally, across a broad range of different payment channels and methods. Nexi’s technological platform and the best-in-class professional skills in the sector lets the company operate at its best in three market segments: Merchant Services & Solutions, Cards & Digital Payments and Digital Banking & Corporate Solutions. Nexi constantly invests in technology and innovation, focusing on two fundamental principles: meeting, together with its partner banks, customer needs and creating new business opportunities for them. Nexi is committed to supporting people and businesses of all sizes, transforming the way people pay and businesses accept payments. It offers companies the most innovative and reliable solutions to better serve their customers and expand. By simplifying payments and enabling people and businesses to build closer relationships and grow together, Nexi promotes progress to benefit everyone.