Swiping the card on the POS machine shows that the card swiping failed, but the money in the card was deducted. What is the reason?

This is a unilateral statement. Your credit card machine belongs to ABC. Your credit card information is first transmitted to the server of ABC, then to the server of UnionPay, and then to the server of BOC for deduction. Then the deduction is fed back from the server of Bank of China to the server of UnionPay, then to the server of Agricultural Bank of China, and finally to your credit card reader. In your case, after the deduction was successful, the deduction was not finally returned to your credit card reader due to communication and other reasons. This kind of unilateral account UnionPay has related operation procedures, and I don't remember the specific details clearly. It seems that the operation should be like this: When the China Bank Account Center reconciled with UnionPay, it was found that the transaction flow was inconsistent and two deductions were made. In this case, the bank's account center reconciler should first check with UnionPay, and UnionPay will transfer the query to ABC, and then ABC and the merchants with credit card machines will reply that there is no commodity transaction, because the credit card is unsuccessful. Then the Agricultural Bank will feed back the information to the Bank of China through UnionPay, and the bank's account center will adjust the two deductions to the card. If the merchant replies that there is a substantial commodity transaction with the customer due to credit card swiping, BOC will inform UnionPay to transfer the money to ABC, which will deposit the money into the merchant's fund account. The specific process may vary from place to place, but the principle is the same.