Under @Event > Check Out Guest (also @Event > Check In Guest) you can add a credit card for a bidder.

If that bidder has a Canadian zip code, you must enter it with a space, for example, K0H 9Z0 in order for RSA to accept it.
If a US client happens to have a one-off Canadian bidder, and they are unfamiliar with the format of Canadian zip codes, they may try to enter this as K0H9Z0. This format is not accepted, and you are not able to add the card if you don't know that you need the space.

To help users have a smoother experience, could we update this error message to have examples of valid zip codes and their formatting, such as:
US: 123456
CAN: A1B 2C3