Invoice and Billing Software Development

I'm looking for a comprehensive invoice and billing software solution that includes a form builder, integrates with payment gateways, and supports multiple user roles.

Key Requirements:
- Form builder for customizable billing forms
- Subscription management features
- Integration with UPI gateway and SmartUpiQR
- User role management: Admin, Editor, Viewer, User

Ideal Skills & Experience:
- Proficiency in software development for desktop platforms (Windows, MacOS, Linux)
- Experience with payment gateway integration, especially UPI
- Strong backend development skills to manage user roles and permissions
- UI/UX design experience for intuitive form building and navigation

Please provide examples of similar projects completed and estimated timelines.