According to the regulations, when the trade credit line of an enterprise is insufficient, it can apply to the foreign exchange bureau for adjusting the basic proportion or single write-off. In principle, the following materials shall be submitted to the foreign exchange bureau: 1, written application; 2. Recent import and export foreign exchange payment/receipt and actual export; 3. Enterprise trade credit registration; 4, the main terms of the enterprise has signed the contract; 5. Other materials required by the foreign exchange bureau, such as the amount of foreign exchange that can be purchased and paid in the verification form system, printed copies of relevant information of the trade credit system, etc. The specific operation is as follows: (1) If the history of import payment is continuous, but the annual payment amount of deferred payment cannot meet the demand, the enterprise may apply to the foreign exchange bureau for adjusting the basic proportion of deferred payment with a written application and relevant materials, or the foreign exchange bureau will confirm the deferred payment. (2) After the enterprise registers the advance payment in the trade credit registration management system, if the export verification system shows that the advance payment receivable foreign exchange quota is insufficient, the enterprise may apply to the foreign exchange bureau for temporary advance payment of foreign exchange quota or increase the basic proportion of advance payment on the basis of written application and relevant materials.