Self-assessed tax recovery demands prior notice before section 79 action when GSTR-1 and GSTR-3B mismatch. Recovery under section 79 applies to unpaid self-assessed tax and interest where tax declared in GSTR-1 is not paid, wholly or partly, through GSTR-3B, including outward supply tax covered by the explanation to section 75(12). The proper officer should first issue a communication requiring payment or an explanation within a reasonable time. If the mismatch is satisfactorily justified or the amount is paid, recovery action need not be initiated.