Is there anyone else in the US Territories that is unable to put their state in?

I was trying to order the new iPhone SE but for some reason, the website doesn't want to take my state abbreviation. I'm from the Northern Mariana Islands and our state is "MP" but it says it isn't valid. Is there anyway I can fix this? Or is it because they don't deliver to our area? I've tried "GU" as well for Guam, but it didn't work either.