Input tax credit reconciliation: require supplier or chartered accountant verification to substantiate ITC claimed when not reflected in purchase statements. Clarification prescribes procedure for reconciling ITC claimed in Form GSTR 3B but not reflected in Form GSTR 2A: tax officers must obtain invoice details, verify section 16 conditions (tax invoice, receipt, payment), assess reversals under sections 17/18 and timeliness under section 16(4), and require verification of supplier tax payment via auditor certificate with UDIN for larger discrepancies or supplier certificate for smaller ones; guidance applies to bona fide errors in FY 2017 18 and 2018 19 and to ongoing or pending proceedings only.