Input Tax Credit verification: require auditor or supplier certification before allowing ITC where GSTR 3B exceeds GSTR 2A. Procedure requires the proper officer to obtain invoices for ITC claimed in FORM GSTR 3B but not reflected in FORM GSTR 2A and verify Section 16 conditions: possession of tax invoice or debit note, receipt of goods or services, and payment of consideration including tax to supplier; check for reversals under Sections 17/18 and time limit compliance under section 16(4). To verify supplier payment of tax, require a CA/CMA certificate with UDIN for larger discrepancies and a supplier certificate for smaller discrepancies; relaxations for certain late claims in FY 2017 18 are restricted by proviso.