Reversal of Input Tax Credit: mandatory reversal where supplier fails to file matching return, with re availment on supplier compliance. Amendments add Rule 37A mandating reversal of input tax credit where the supplier has not filed the corresponding FORM GSTR-3B by the stipulated cutoff and permitting re availment if the supplier later files; introduce Rule 88C requiring system intimation (FORM GST DRC-01B) when outward-supply declarations exceed GSTR-3B liability and prescribing payment or explanation via FORM GST DRC-03/Part B within a short period with recovery under section 79 for non-compliance; substitute Rule 109 and insert Rule 109C to standardise appeal filing, acknowledgments and withdrawal; and revise multiple forms and GSTR-1 tables to capture e commerce reporting, invoice particulars, refund documentation and PAN-linked verification.