ISD Return compliance requires invoice-level inward supply reporting and an ISD ledger, with late filing subject to fees. A valid ISD Return requires taxpayer identifiers, the tax period, and final invoice-level inward supply data for goods and services claimed as ITC, auto-populated from the counterparty supplier but modifiable by the taxpayer; recipients may add invoices they possess. The return must list invoice details with the GSTIN of the credit receiver and include an ISD Ledger showing Opening Balance of ITC (auto-populated), credits for services received, debits for ITC reversals and distributions, and a Closing Balance. Monthly filing is required with late filing allowed on payment of fees.