It has always been GSTR-1 and 3B's mismatch that has been the Achilles' heel of GST. Several cases have been reported where the supplier transferred ITC through GSTR-1 even before taxes were refunded via GSTR-3B. There are discrepancies between GSTR-1 and 3B, some of which are due to tax payments, while others may be due to errors that result in tax payments not being made. ITC mismatch between GSTR-1 and GSTR-3B is now covered by GST rule 88C. We have also mentioned the deadline, opportunity, backdrop, etc. https://blog.saginfotech.com/gst-rule-88c