Vyapar Billing Data Retrieval Tool

I need a robust, secure solution that can log in to an authorised Vyapar account, pull every piece of billing-related information, and let me export it in the formats I actually use day-to-day. The core data set includes invoices, purchase bills, individual product rates and quantities, customer & vendor details, taxes, discounts and any other fields Vyapar exposes.

Scope of extraction
• Source environments: Web and Desktop instances of Vyapar.
• Target formats: clean, well-structured Excel, CSV and JSON files ready for downstream analysis or direct import into other systems.
• Platform choice: I am flexible—build a Windows desktop app, an Android utility, an iOS companion, or even a cross-platform service; choose the avenue that achieves the fastest, most reliable sync.

Key expectations
• Authorisation flow that respects Vyapar’s security model.
• Incremental as well as full data pulls.
• Error logging and clear status reporting so I always know what has synced.
• A simple UI (or command-line flags if you opt for a headless tool) where I can enter credentials, pick a date range and hit “Export”.
• Well-commented code and build instructions so I can extend the tool later.

Acceptance criteria
1. Connects to a live Vyapar account (demo credentials will be supplied) and retrieves at least 500 real records without data loss.
2. Generates identical totals for at least three random invoices when cross-checked manually.
3. Produces downloadable files in Excel, CSV and JSON on demand.
4. Runs error-free on the chosen platform in a fresh install scenario.

If you have experience with REST APIs, desktop connectors (.NET/WPF, Electron), mobile stacks (Kotlin/Swift), database handling (SQLite, SQL Server) or cloud sync engines, you’ll feel right at home. Let me know your proposed architecture and turnaround time; I’m ready to get started.