Determination of unpaid or wrongly claimed input tax triggers a show-cause notice requiring tax, interest, and potential penalty. Determination of tax not paid, short paid, erroneously refunded, or input tax credit wrongly availed or utilised (except for fraud or willful misstatement) proceeds by service of a show-cause notice requiring payment of specified tax with interest and penalty. Notices must be issued three months before the limitation, additional statements may extend to other periods on same grounds, and voluntary payment of tax with interest before notice halts proceedings for that amount. Payment within thirty days of notice avoids penalty; otherwise the proper officer determines tax, interest and penalty and must issue an order within a three-year limitation period.