legal analysis: if the customer's invoice is lost, the merchant shall not issue the corresponding invoice repeatedly. Generally, if the customer is an individual, the merchant can copy the invoice and affix the official seal to confirm it. If the customer is an enterprise unit, the merchant should handle the corresponding tax payment certificate and the corresponding tax procedures according to law. Legal basis: Article 19 of the Measures for the Administration of Invoices of the People's Republic of China. Units and individuals that sell goods, provide services and engage in other business activities collect money from foreign businesses, and the payee shall issue invoices to the payer; Under special circumstances, the payer will issue an invoice to the payee. Twentieth all units and individuals engaged in production and business activities in the purchase of goods, services and other business activities to pay, should obtain invoices from the payee. When obtaining an invoice, it is not allowed to change the name and amount.