Tax invoice rules: timing and content requirements govern issuance, revisions, and special cases for continuous and exempt supplies. Tax invoice rules set timing and content obligations: for goods, invoices are required before or at removal or delivery; for services, within a prescribed period before or after provision. Invoices must show description, quantity (where applicable), value, tax charged and prescribed particulars. Special provisions govern revised invoices after registration, bills of supply for exempt supplies, receipt vouchers for advances, invoicing for supplies received from unregistered persons, and distinct invoicing rules for continuous supplies and supplies sent on approval.