Senior .NET Developer – Financial Systems & Integrations

ASSYST, Inc. • Sterling, VA

1d

About The Position

ASSYST is seeking a highly skilled and self-driven Senior Software Developer to support and enhance complex, enterprise-scale financial applications. This role involves working on custom-built systems handling high-volume transactions, including payments, reconciliation, reporting, and multi-system integrations.
The ideal candidate is detail-oriented, capable of working independently, and experienced in solving complex financial and technical challenges.

Requirements

• 7+ years maintaining legacy applications with limited documentation
• 7+ years developing Finance-Tech solutions (payments, billing, reconciliation)
• 5+ years integrating with Tyler Technologies MUNIS or similar ERP systems
• 3+ years recent experience with Paymentus integrations (iframes, redirects, UAT/production)
• 7+ years UI/UX development with responsive design (recent experience required)
• Proven ability to work independently and deliver practical solutions
• HTML, CSS, JavaScript (Bootstrap or Tailwind)
• Responsive and mobile-first UI/UX design
• C#, ASP.NET (WebForms, MVC, .NET Core)
• Azure Entra ID / Azure AD B2C
• Microsoft SQL Server
• System integration (API, DB, file-based)
• Microsoft DevOps & system administration (IIS, networking)
• Familiarity with AI-assisted development

Responsibilities

• Maintain and enhance legacy and custom financial applications
• Analyze and modify application logic with minimal documentation
• Design and develop scalable software solutions and integrations
• Implement API, database, and file-based system integrations
• Improve UI/UX with modern, responsive design practices
• Troubleshoot and resolve complex financial system issues
• Collaborate with technical teams and document solutions

What This Job Offers

• Job Type: Full-time
• Career Level: Mid Level
• Education Level: No Education Listed
• Number of Employees: 101-250 employees