Determination of tax liabilities: show-cause notice, voluntary payment to avoid penalty, orders subject to a three-year limit. Determination of tax not paid, short paid, erroneously refunded or input tax credit wrongly availed or utilized (excluding fraud or willful misstatement) is initiated by a show-cause notice from the proper officer requiring payment of tax, interest and penalty; notice timing, extension by statement for same grounds, voluntary pre-notice payment to avoid proceedings, penalty waiver for payment within thirty days of notice, and a three-year limitation for issuance of the final order are prescribed.