Tax invoice requirements under GST: mandatory invoice fields, HSN digit thresholds, export endorsements, and e invoice/QR code obligations. Tax invoices must include supplier details and GSTIN, unique serial number, date, recipient identification (GSTIN or name/address with state/code per value and situational rules), HSN/SAC code, description, quantity/unit, taxable and total values, tax rates and amounts by component, place of supply and state for inter state supplies, delivery address if different, reverse charge indication, and supplier signature or digital signature except where an e invoice with IRN/QR is issued; QR code requirement and HSN digit reporting thresholds tied to turnover and return Table 12 obligations also apply.