Determination of tax evasion triggers notice, interest and penalty with avenues for voluntary payment to conclude proceedings. The proper officer may serve a notice when tax is unpaid, short paid, erroneously refunded or input tax credit wrongly availed by reason of fraud, willful misstatement or suppression of facts, requiring payment of specified tax with interest and a penalty equivalent to the tax; voluntary payment with interest and a reduced penalty before notice or prompt payment within thirty days after notice or order can conclude proceedings, subject to limitation periods and exceptions for criminal proceedings.