Tax invoice requirements set mandatory invoice content and timing, including special export endorsements and service invoice deadlines. Tax invoice requirements prescribe mandatory contents including supplier and recipient identification (GSTIN if registered), unique consecutive serial number for the financial year, date, description, taxable value after discounts, tax rates and amounts, HSN or Accounting Code, quantity or unit for goods, place of supply and delivery where applicable, reverse charge indication, revised or supplementary invoice marking where relevant, signature of supplier, and export invoice endorsements; service invoices must be issued within specified timeframes, with extended periods for continuous supplies and for banking and financial institutions.