Tax invoice requirement: issue before or at supply for goods and within prescribed period for services. A registered person must issue a tax invoice for taxable goods and services with timing rules tied to removal, delivery, provision or prescribed periods; invoices must show prescribed particulars including description, quantity, value and tax charged. The Government may notify categories for special invoice treatment. Exceptions allow revised invoices after registration, exemption for low-value supplies, bills of supply for exempt or composition-scheme supplies, receipt and refund vouchers for advance payments, and invoice/payment voucher obligations where reverse charge applies. Continuous supplies require invoicing with each statement, payment, due date or event completion.