Tax invoice rules: timing, alternative documents and special vouchers govern issuance and documentation for taxable supplies and advances. Registered persons supplying taxable goods must issue a tax invoice at removal, delivery, or when goods are made available, showing description, quantity, value, tax and prescribed particulars; suppliers of taxable services must issue a tax invoice within a prescribed period showing description, value, tax and prescribed particulars. The Government may notify categories where alternate documents suffice or where tax invoices need not be issued. Exceptions and mechanisms include revised invoices after registration, low-value supply thresholds, issuance of a bill of supply for exempt or composition supplies, receipt and refund vouchers for advances, reverse-charge invoicing and payment vouchers, and special timing rules for continuous supplies, cessation, and approval sales.