Determination of unpaid GST liability: notice, interest and penalty consequences for non-payment and voluntary correction. Where the proper officer finds tax not paid, short paid, erroneously refunded or input tax credit wrongly availed (except for fraud or wilful suppression), he shall serve a show cause notice requiring payment of tax with interest and a penalty. Notices must be issued at least three months before the time-limit for orders; statements extending identical grounds to other periods are deemed notices. Voluntary payment of tax with interest before notice prevents issuance of notice for that tax, subject to deficiency. Payment within thirty days of the show cause notice removes penalty. The officer shall determine tax, interest and penalty and issue an order within three years from the annual-return due date or erroneous refund date.