1. There are two kinds of export invoices, one is a commercial invoice, which is used to sign contracts with foreign businessmen, and the other is an export invoice supervised by the tax authorities. This kind of invoice can be issued after you have export-related information at your electronic port, and the accounts can be handled accordingly; 2. Write-off refers to the write-off of foreign exchange income, which can only be processed after the foreign exchange is collected. When a bank receives foreign exchange, it needs your verification slip number (issued by SAFE), invoice number (both invoice numbers are acceptable), exporting country, trade type, etc. The most important thing is your enterprise's electronic port card, and then the bank will give you a receipt before you can write it off online.