GST Billing Software & Panel

I need a lightweight GST-compliant billing solution tailored for a service-based business. The system should include both a web-based admin panel and an Android APK so that I can create invoices from my laptop while my staff can do the same from their phones. Core workflow • Admin and staff must be able to generate GST invoices, instantly turn them into professionally formatted PDFs, and share those PDFs via WhatsApp, email, or any common channel. • All invoices should auto-save in a searchable history for easy reference and summary reports. • Basic client data (name, GSTIN, address, contact) should populate automatically when selected, cutting down on manual entry. Access & roles One login for me as super-admin and separate logins for staff, each limited to invoicing only. I should retain full control over user creation, password resets, and viewing every invoice generated. Tech expectations Clean, responsive admin UI (React, Angular, or similar) and a stable Android APK (native Java/Kotlin or Flutter). A straightforward database schema—MySQL, PostgreSQL, or Firebase—is fine as long as backups and export options are included. Deliverables 1. Web admin panel, fully deployed 2. Signed Android APK ready for Play Store upload 3. Source code with setup instructions 4. Brief video or live demo showing invoice creation and PDF sharing in action If any open-source libraries or SaaS APIs are used, please note them up front so licensing is clear. Looking forward to a quick turnaround and a smooth user experience.