Input Tax Credit reconciliation: procedures to verify and substantiate GSTR 3B vs GSTR 2A discrepancies and admit valid ITC claims. The proper officer shall obtain invoice details for ITC claimed in FORM GSTR-3B but not appearing in FORM GSTR-2A and verify Section 16 eligibility: possession of tax invoice/debit note, receipt of goods or services, and payment including tax; and assess reversals under Sections 17 or 18 and time limit under Section 16(4). To verify supplier payment of tax, where the supplier wise difference for the year exceeds a monetary threshold, a CA/CMA certificate with UDIN is required; for differences up to the threshold, a supplier's certificate is acceptable.