1. Card swiping is restricted: for example, a credit card has a daily limit, so when the consumption has reached the limit, even if there is a limit in the card, you can't swipe the card.

2. The card is frozen: for example, if it is frozen by the bank, even if there is a limit in the user's card, it is impossible to swipe the card. You need to contact the issuing bank to inquire about the specific reasons for freezing, and then do further processing.

3. Password error: if the transaction password is entered incorrectly, the card will not be able to pay for the transaction, and the line will not be used.

4. There is something wrong with the POS machine: If there is nothing wrong with the credit card, it is also possible that the POS machine of the merchant is out of order and cannot be used.

5. The transaction is risky: if the transaction is suspected to be risky by the bank, the bank will not let the user successfully conduct the transaction in order to avoid the risk.