1. First, check the validity period of the credit card. If the credit card expires, you need to contact the bank for renewal or replacement.

2. Secondly, check the power supply of the POS machine. If the POS machine has no electricity, it is impossible to conduct credit card transactions. You need to recharge or replace the battery, and then restart the POS machine. Sometimes restarting the POS machine can solve some temporary problems.

Finally, make sure that the credit card has not been frozen or lost. If there is a problem with the credit card, you need to contact the bank for handling.