If you have a customer who's trying to pay you with a credit card that has an address located outside the United States, they may have a ZIP code (or Province code) that includes characters that doesn't meet the U.S. 5 digit standard.
In most cases the international card holder is provided with information by the card issuing entity regarding how to process in the United States when they are presented with this situation.
For transactions that have problems due to such a zip code situation, your customer should 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.
Intuit's payment processing doesn't utilize an alphanumeric zip code field. It's up to the credit card holder in conjunction with their credit card issuing bank, to provide credit card information that would be compatible in the U.S. for processing.
If the International credit card cannot be used, another form of payment will be required.