Discrepancy in output tax liability: electronic notice compels supplier and recipient to rectify returns or face automatic reversal. Former Rule 75 required electronic communication of discrepancies in claims for reduction of output tax liability to supplier and recipient via portal forms, allowing suppliers to correct outward-supply details and recipients to correct inward-supply details in the month notified; if unrectified, the discrepancy amount was added to the supplier's output tax liability, debited to the electronic liability register and reflected in the supplier's next monthly return.