I have not completed the booking. However, I was still charged by my credit card company.
Even if an error message was indicated, the booking still might have been completed. Please check the status of your booking on the website just in case. Please be noted that we will check your account balance and get authorization for the transaction from your credit card company, when you tried to book. The amount of the travel fee may remain in your account, even if the reservation was not completed. And the usage limit for the credit card may be decreased for a while. However, we give all finalized transaction data to the credit card company on the next day of transaction, then, credit card company actually invoices you. If the booking had not been completed, the charge will disappear later.