UPS throws a postal code error when trying to purchased a label to Japan, asking for a 0 to 5 character postal code. Japan has a 7 digit postal code. The address was verified by ShipStation and Melissa Lookups. ShipStation support said there is a complicated work around that requires senior support (they are making the label for me currently). It was suggested that I post the problem here in hopes to have it solved in a feature update. Seems like a pretty big problem - you can't buy UPS labels to Japan !?!?
Erin, thank you for the response. Ultimately, Nagano was changed to NNG and the label went through. I have not been able to find a table that shows NNG and other state codes. I found a table that says Nagano would be OU, which I had tried early on (and failed). Shipstation support gave me a link to a table of prefectural codes, not state codes. I did find one table of state codes from GMAC, but it lists Nagano as NGN, not NNG.
Thanks for getting back to me about this. This is not an official ShipStation endorsed resource but I was able to find a table from the United Nations Economic Commission for Europe that lists the trade and transport location codes.
Hopefully this helps you out in the future.
-Erin: Your Friendly Neighborhood ShipStation Community Manager