Tax invoice requirements: timing, exceptions and vouchers determine GST invoicing obligations and alternate documents under the regime. A registered supplier must issue a tax invoice for taxable goods at or before removal or delivery and for taxable services within a prescribed period, showing prescribed particulars. The Government may notify categories where other documents are treated as invoices or invoices need not be issued. Exceptions include revised invoices within one month of registration certificate, a low value exemption for supplies below two hundred rupees, bills of supply for exempt or composition supplies, receipt and refund vouchers for advance payments, and specific invoicing and payment voucher duties where reverse charge applies; continuous supply rules govern timing tied to statements, payments, contractual due dates, events, or cessation.