Determination of unpaid tax: notice and recovery framework prioritises payment, interest, and prescribed penalty consequences. Determination of unpaid or short paid tax and wrongly availed or utilised input tax credit (excluding fraud or wilful misstatement) is made by a show cause notice requiring payment of tax, interest under section 50 and a penalty. The officer must issue the notice at least three months before the assessment time limit, may serve a deemed notice statement for additional periods on the same grounds, and must issue an order determining tax, interest and a prescribed penalty within three years from the due date for the annual return or from the date of erroneous refund. Payment within thirty days of notice avoids penalty.