Compounding scheme requires simplified quarterly returns and fixed-rate tax payment without input tax credit, with purchase and import declarations. Compounding taxpayers opting for a fixed-rate scheme must file a simplified quarterly return (GSTR-4) reporting total value of supplies, tax at the compounding rate, payment details, invoice-level purchase information (auto-drafted from counter-party uploads), and imports; they may export and may be subject to rules limiting purchases to tax-paid supplies and reverse-charge purchases from unregistered suppliers.