Input tax credit discrepancy requires payment or explanation to address excess ITC, with interest and possible tax demand. A system-generated FORM GST DRC-01C notifies taxpayers when ITC claimed in FORM GSTR-3B exceeds ITC available in FORM GSTR-2B and requires either payment of the excess with interest via FORM GST DRC-03 or a reasoned reply in Part B within seven days; listed grounds for discrepancy include delayed receipt of supplies, inadvertent omissions, import or SEZ credits not reflected in GSTR-2B, reclaims of prior reversals, supplier filings, or corrections in subsequent returns, with unpaid or unexplained balances subject to tax demand procedures.