However, in case of sales discount, the original invoice can be recovered and marked as "invalid" and then reissued, or a red-ink invoice can be issued after obtaining the other party's valid certificate. Legal basis: Article 27 of the Detailed Rules for the Implementation of the Measures for the Administration of Invoices in People's Republic of China (PRC). After the invoice is issued, if it is necessary to issue a red-ink invoice for sales returns, the original invoice must be recovered and marked as "invalid" or a valid certificate from the other party must be obtained. After issuing the invoice, if there is a sales discount, you must reissue the sales invoice after recovering the original invoice and marking it as "invalid" or issue a red-ink invoice after obtaining the valid certificate from the other party.