The validation that is run against ZIP codes does in the system does not accept characters and is limited to 5 digits. Unfortunately, the components of some non US ZIP codes may contain letters and exceed the 5 digit max.
To workaround this the customer will enter the first three numeric digits of their ZIP code and then add "00" to the end. Linked below is an article explaining the solution in further detail.
For additional support please click on the support button at the bottom of this article and open a ticket with our team.