Tax Invoice requirements govern issuance timing, exceptions, and remedies including credit notes and refund vouchers. Tax invoice rules require registered suppliers to issue tax invoices at removal or delivery of goods and before or within a prescribed period for services, with specified exceptions and alternative documents: bill of supply for exempt or composition supplies, receipt and refund vouchers for advances, payment vouchers and invoices under reverse charge, and revised invoices covering pre-registration supplies. Continuous supply, event-linked payments, and approval-for-sale arrangements have specific timing rules. Invoice contents include supplier and recipient identification, serialisation, HSN/SAC, taxable value, tax amounts, place of supply, reverse charge indication, signature, and IRN/quick reference or prescribed declaration where applicable.