If you are placing an on-line order for the first time, the system will verify that the billing address AND zip code match the ones that the credit card issuing institution has on file. This information is checked for your protection, and to prevent on-line credit card fraud. Even if the credit limit allows the purchase, your order will not be authorized unless the address verification checks out positive.
Be sure to double check your expiration date and the 3 digit verification code for Visa, Mastercard, Discover, and the four digit code found on the front of the American Express card. Still have problems? Call your bank or credit card company. You can usually find the number on the back of your credit card.