Senior Software Engineer

onPhase is seeking an experienced Senior Software Engineer to join their software development team working on mission-critical financial technology applications. The role involves developing and maintaining large-scale systems for invoice processing and accounts payable, requiring a strong understanding of financial workflows.

Responsibilities:

• Developing and maintaining large-scale invoice processing, accounts payable, and document management systems serving enterprise clients across multiple industries

Requirements:

• Hands-on experience in financial or B2B software
• Strong understanding of AP/AR workflows
• Payments systems knowledge
• Broader Finance domain processes understanding
• Accounts Payable (AP) and/or Accounts Receivable (AR) software development or operational systems experience
• Payments platforms including ACH, wire transfer, virtual card, and payment processing workflows experience
• Invoice processing, purchase orders, remittance processing, and B2B document exchange (EDI) experience
• Financial Technology (FinTech) products serving enterprise or mid-market clients experience
• ERP integrations — SAP, Oracle, NetSuite, QuickBooks, Microsoft Dynamics, or similar platforms experience
• Audit trail design, financial data integrity, and compliance-aware software development experience
• Spend management, treasury operations, or general ledger (GL) system connectivity experience
• Advanced C# and VB.NET proficiency — mixed-language enterprise codebase
• .NET Framework 4.6–4.8 — extensive experience with legacy .NET Framework applications
• .NET 6/7/8 — modern .NET development for new platform initiatives experience
• ASP.NET Web Forms and MVC — maintain and enhance hybrid web applications experience
• ASP.NET Web API — build and maintain RESTful services and integrations experience
• Entity Framework — data access and ORM patterns (Code First and Database First) experience
• Windows Services — background processing services for document workflow automation experience
• Blazor Server — build modern web UIs for SaaS platform experience
• AngularJS — maintain existing frontend components experience
• JavaScript/jQuery — legacy frontend maintenance with jQuery UI and validation experience
• XSLT transformations — XML-based templating systems experience
• Telerik UI Components — enterprise UI components for legacy and modern applications experience
• OAuth 2.0 & JWT — modern API authentication and security experience
• SQL Server — complex stored procedures, functions, and database design experience
• Database-first development — schema changes, migrations, and performance optimization experience
• ADO.NET — custom data access patterns and legacy integration experience
• Amazon S3 — cloud document storage and management experience
• Multi-tenant SaaS architecture — customer-specific configurations and customizations experience
• EDI processing — Electronic Data Interchange (810, 850, 855, 856 transaction sets) experience
• File processing — CSV, XML, fixed-width file imports/exports experience
• SOAP/REST web services — external system integrations experience
• Payment processing integrations — financial system connectivity experience
• MSBuild and Visual Studio — build automation and deployment experience
• IIS deployment and management — Windows-based web application hosting experience
• Git version control — large enterprise codebase management experience
• PowerShell scripting — deployment and automation tasks experience
• Azure DevOps Pipelines — CI/CD with YAML configurations and automated testing experience
• NuGet Package Management — private Azure Artifacts feeds and dependency management experience
• Bachelor's degree in Computer Science or related discipline
• 5+ years of .NET development experience
• Finance/FinTech background — hands-on AP, AR, Payments, or financial software experience strongly preferred
• Strong SQL Server database design and optimization skills
• Self-motivated with ability to navigate complex, large codebases
• Strong problem-solving skills for debugging and optimizing enterprise applications
• Excellent communication skills for collaborating with business stakeholders and QA teams
• Experience with legacy modernization and gradual migration strategies