Tax collected but not paid requires immediate remittance to government; notice, interest and adjustment mechanisms apply. Section 76 requires persons who have collected amounts as tax but not paid them to the Government to forthwith remit those amounts regardless of the taxability of the supplies. The proper officer may issue a show cause notice, determine the amount due after considering representations, and require payment; interest at the rate under section 50 accrues from collection to payment. A hearing must be granted if requested, and the officer must issue a reasoned order within one year (excluding judicial stays). Payments are adjustable against tax liability and any surplus is credited or refunded under the refund procedure.