Using your credit card internationally:

Validation of international credit cards often presents difficulties for US based businesses. Zipcodes including letters or that are not equal to five digits will be declined.

For transactions that have problems due to such a zip code situation, the card holder will need to contact the card issuing bank to determine if there are options for using their international card with U.S. based businesses that require a 5-digit numeric zip code. It is the responsibility of the card holder to provide such information when processing an international card.