Input tax credit usage: electronic credit ledger funds output tax but excludes liabilities under reverse charge. The electronic credit ledger records self-assessed input tax credit credited from returns and may be applied to output tax liabilities under CGST/SGST/UTGST/IGST subject to statutory conditions; ITC in the ledger cannot be used for tax payable under the reverse charge mechanism. Statutory provisions and guidance prescribe a hierarchical order of utilisation across IGST, CGST, SGST and UTGST, and Rule 86 mandates ledger maintenance in FORM GST PMT-02, automatic debits on liability discharge and refund claims, re-credit upon refund rejection, prohibition of direct entries, and reporting discrepancies via FORM GST PMT-04.