USPS carriers only have the provision to do shipping to military bases of United States. UPS and Fedex carriers cannot be used to ship items to these areas. The provinces include Armed Forces Europe, Armed Forces America and Armed Forces Pacific.
For Sales orders synced via connectors to NetSuite, error will be thrown like Invalid shipping taxcode and might reference to set the default taxcode. Initially check whether the province is a military base area and NetSuite have native integration with USPS. If not, setup the USPS carrier in the account.