This type of an error is common when the billing information you have entered at checkout does not match the billing information on file for the card you are using. The billing address automatically defaults to being the same as the shipping address! You may need to update the billing information at checkout by un-checking the box for "use my shipping address" and changing the billing information to the billing address that matches whats on file with your bank or credit card company! If you have an account, you can select an address from your saved addresses or you can add a new one by entering the information and clicking UPDATE. If you do not hit update, the information is not saved and will not allow the transaction to complete properly.
If it still doesn't work after updating the billing information, we recommend you reaching out to your bank or card company to verify the information they have on file or see if they are declining the transaction.