This document provides a comprehensive overview of the Goods and Services Tax (GST) e-invoicing implementation. It clarifies the mandatory requirements for valid invoices, including the Invoice Reference Number (IRN) and QR code, effective from October 1st, 2020. The guide also distinguishes between B2B and B2C QR codes, explaining their purposes and applicability. It addresses common queries regarding e-invoice generation, signing, amendments, and integration with e-way bills, making it an essential resource for businesses navigating these new regulations.