The credit card invoice voucher must be stamped. According to relevant query information, the credit card invoice voucher is a shopping voucher provided by the bank to the cardholder, including transaction details, consumption date, merchant name, transaction amount and other information. In order to ensure the authenticity and validity of the voucher, it is usually necessary to stamp the voucher to indicate the authenticity and validity of the voucher. At the same time, stamping can also prevent credentials from being tampered with, copied or used fraudulently. Therefore, when using a credit card invoice voucher, it is recommended to check whether there is a stamp from a formal institution on the voucher. If the voucher is not stamped, you can contact the card-issuing bank or merchant for a replacement.