Looks nice, kudos for offering it for free - 5$/month is still not nothing. It would be grand if you included "US" somewhere besides the domain, because the service geolocates US zipcodes, not international zip codes.
I'm not saying they don't exist, but I'm not sure I've ever seen one.
The US-based organizations using the term "zip code" for non-US addresses are doing so either out of ignorance or expediency, since fitting "zip/postal code" into a space is sometimes not possible.
That doesn't make it correct, and I don't believe that some peoples unequivocally wrong usage of a term should oblige other people to qualify their correct and unambiguous usage of it.
As a recent example, see KanbanFlow for example https://sites.fastspring.com/kanbanflow/order/customer
The "Zip code" input field is simply hard coded for every country.