Senior Software Engineer

onPhase; Town of Florida (NY); On-site; USD 120,000 - 190,000; Full time

Job summary

onPhase is seeking an experienced Senior Software Engineer to join our software development team building mission-critical financial technology applications. You will develop and maintain large-scale invoice processing, accounts payable, and document management systems for enterprise clients across industries.

The ideal candidate has hands-on FinTech experience, strong knowledge of AP/AR workflows, payments, ERP integrations, and modern .NET technologies including C#, VB.NET, ASP.NET Web API,

Qualifications

• Bachelor's degree in Computer Science or related discipline.
• 5+ years of .NET development experience.
• Finance/FinTech background with AP/AR or payments experience preferred.
• Strong SQL Server design and optimization skills.
• Ability to navigate large, complex codebases and debug effectively.
• Excellent communication with stakeholders and QA teams.

Responsibilities

• Develop and maintain large-scale invoice processing, accounts payable, and document management systems for enterprise clients.
• Collaborate on AP/AR workflows, payments platforms, and ERP integrations (SAP, Oracle, NetSuite, QuickBooks, Microsoft Dynamics).
• Contribute to design of audit trails, data integrity, and compliant software development.
• Build and enhance RESTful services using ASP.NET Web API and modern .NET technologies.
• Work with Azure DevOps for CI/CD, testing, and deployment.

Skills

C#

VB.NET

ASP.NET Web API

Entity Framework

SQL Server

Azure DevOps

Windows Services

Blazor

AngularJS

OAuth 2.0

Education

Bachelor's degree in Computer Science or related

Tools

Visual Studio

MSBuild

IIS

Azure DevOps Pipelines

Job description

We are seeking an experienced Senior Software Engineer to join our software development team working on mission-critical financial technology applications. You will be responsible for developing and maintaining large-scale invoice processing, accounts payable, and document management systems serving enterprise clients across multiple industries. The ideal candidate brings hands-on experience in financial or B2B software, with a strong understanding of AP/AR workflows, Payments systems, and broader Finance domain processes.

Finance Domain Experience - Strongly Preferred:

Given the nature of our core products — invoice processing, vendor payment management, and AP automation — we place significant value on candidates with real-world experience in:

• 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 — 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

Technical Skills:

Core .NET Technologies

• 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
• ASP.NET Web Forms and MVC — maintain and enhance hybrid web applications
• ASP.NET Web API — build and maintain RESTful services and integrations
• Entity Framework — data access and ORM patterns (Code First and Database First)
• Windows Services — background processing services for document workflow automation

Web Technologies

• Blazor Server — build modern web UIs for SaaS platform
• AngularJS — maintain existing frontend components
• XSLT transformations — XML-based templating systems
• Telerik UI Components — enterprise UI components for legacy and modern applications
• OAuth 2.0 & JWT — modern API authentication and security

Database & Data Technologies

• SQL Server — complex stored procedures, functions, and database design
• Database-first development — schema changes, migrations, and performance optimization
• ADO.NET — custom data access patterns and legacy integration
• Amazon S3 — cloud document storage and management
• Multi-tenant SaaS architecture — customer-specific configurations and customizations
• EDI processing — Electronic Data Interchange (810, 850, 855, 856 transaction sets)
• SOAP/REST web services — external system integrations
• Payment processing integrations — financial system connectivity

DevOps & Infrastructure

• MSBuild and Visual Studio — build automation and deployment
• IIS deployment and management — Windows-based web application hosting
• PowerShell scripting — deployment and automation tasks
• Azure DevOps Pipelines — CI/CD with YAML configurations and automated testing
• NuGet Package Management — private Azure Artifacts feeds and dependency management

Preferred Qualifications:

• 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