Senior Software Engineer

onPhase Software is hiring a Senior Software Engineer to work on financial technology applications. The role sits on a software development team building and maintaining large-scale invoice processing, accounts payable, and document management systems for enterprise clients across multiple industries. It is a fit for an engineer with hands-on financial or B2B software experience and a working knowledge of AP/AR workflows, payments systems, and finance domain processes.

What you will do

• Develop and maintain large-scale invoice processing, accounts payable, and document management systems
• Build and maintain RESTful services and integrations with ASP.NET Web API
• Maintain and enhance hybrid web applications built with ASP.NET Web Forms and MVC
• Build modern web UIs for the SaaS platform with Blazor Server
• Maintain existing frontend components in AngularJS, JavaScript, and jQuery
• Write complex SQL Server stored procedures, functions, and database design
• Handle schema changes, migrations, and performance optimization in a database-first setup
• Work with multi-tenant SaaS architecture, including customer-specific configurations and customizations
• Process EDI transactions (810, 850, 855, 856) and handle CSV, XML, and fixed-width file imports and exports
• Integrate with external systems through SOAP/REST web services and payment processing connections
• Manage background processing services for document workflow automation using Windows Services
• Work with build automation and deployment using MSBuild, Visual Studio, IIS, PowerShell, and Azure DevOps Pipelines
• Manage dependencies through NuGet and private Azure Artifacts feeds
• Collaborate with business stakeholders and QA teams

What they are looking for

• Advanced C# and VB.NET proficiency in a mixed-language enterprise codebase
• Extensive experience with .NET Framework 4.6–4.8 legacy applications
• Modern .NET development experience with .NET 6/7/8
• Entity Framework data access and ORM patterns, both Code First and Database First
• XSLT transformations for XML-based templating systems
• Telerik UI Components for legacy and modern applications
• OAuth 2.0 and JWT for API authentication and security
• ADO.NET custom data access patterns and legacy integration
• Amazon S3 for cloud document storage and management
• Git version control in a large enterprise codebase
• 5+ years of .NET development experience
• Bachelor's degree in Computer Science or a related discipline
• Strong SQL Server database design and optimization skills
• Self-motivated with the ability to work through complex, large codebases
• Strong problem-solving skills for debugging and optimizing enterprise applications
• Excellent communication skills for working with business stakeholders and QA teams
• Experience with legacy modernization and gradual migration strategies

Finance domain experience strongly preferred

The core products are invoice processing, vendor payment management, and AP automation, so real-world experience in any of these areas carries weight:

• Accounts Payable (AP) and/or Accounts Receivable (AR) software development or operational systems
• Payments platforms including ACH, wire transfer, virtual card, and payment processing workflows
• Invoice processing, purchase orders, remittance processing, and B2B document exchange (EDI)
• Financial Technology (FinTech) products serving enterprise or mid-market clients
• ERP integrations with SAP, Oracle, NetSuite, QuickBooks, Microsoft Dynamics, or similar platforms
• Audit trail design, financial data integrity, and compliance-aware software development
• Spend management, treasury operations, or general ledger (GL) system connectivity

Location

This role is based in the United States.