For the countries having similar country codes, like US and Canada or others, you need to use a country ID when sending request or getting available areas. The ID of each country id unique.
This ID is sent along with the country codes and names when you request for available
For details please check this page:
When you request for areas you must send that country ID to distinguish the country from those having same country code. Please check this page:
as you can see the last argument of the function is country ID.
This can be used to get areas like USA, Canada, Jamaica etc, as they have same country code ‘1’, but their IDs are unique so that they can be used to get their areas only.