Input tax credit mismatch: verify documentary evidence and require certified confirmations to validate ITC claims. Where recipients claimed ITC in GSTR-3B that does not appear in GSTR-2A due to supplier non-filing, misreporting, wrong GSTIN or wrong classification, the proper officer shall obtain invoice details and verify statutory ITC conditions: possession of tax documents, receipt of goods or services, payment to supplier, timeliness, and any requirement for reversal. For verification of supplier tax payment, documentary certification is required-externally certified CA/CMA certificates with UDIN for larger discrepancies or supplier certificates for smaller ones-and these measures apply to bona fide errors in the specified financial years in ongoing or pending proceedings.