Hi DoyeongJung
We also have an English SBB community. Please try to post your queries in the correct community language so that other users can benefit from a research.
For data protection reasons, we have no way of checking why the payment method you are currently using for the purchases in our online platforms has been declined.
To find out what exactly the problem is, we ask you to contact your credit card administrator or your bank. Otherwise, we advise you to use another payment method.
Have a nice day. EllenvS.