For the purpose of computing and paying any drawback claimed and payable upon any goods duly entered, shipped, and exported, a debenture shall in due time after such entry be prepared by the collector or other proper officer; certifying in the first instance the entry outwards of such goods; and so soon as the same shall have been duly exported, and a notice containing the particulars of the goods shall have been delivered by the exporter to the export officer, the shipment and exportation thereof shall be certified upon such debenture by the export officer, and the debenture shall thereupon be computed and passed with all convenient despatch.