An invoice is an important payment document that can be used to acknowledge receipt of payment and related tax matters after the purchase of goods or services. In some cases, some invoices may not be stamped. In this case, it is most likely due to the invoice issuer forgetting to stamp the invoice or having a faulty seal. However, in the absence of a stamp, the validity of the invoice can cause problems as it is difficult to determine its authenticity.

Whether an invoice without a stamp is valid is a matter of much debate. According to the State Administration of Taxation (SAT), an unstamped invoice does not affect its validity, but it is important to note that in order to avoid being considered a forged or invalid invoice, it is advisable to carry out a check with the seller in a timely manner after confirming the transaction to ensure that the invoice is genuine and reliable.

When encountering an unstamped invoice, we should contact the other party as soon as possible. The first step is to find out about the other party's stamp, as well as to confirm whether they are willing to make up the stamp. After confirming that the other party is willing to make up the stamp, in order to avoid possible problems in the future, the invoice should be kept safe and the relevant account information should be properly recorded in order to prevent any errors from occurring.