If a claim is sent that has a patient address outside of the United States, United States Territory, or Canada, a country code (2 letter abbreviation) is required. If the patient address is within the United States, United States Territory, or Canada then a country code is not required. To fix this rejection, return to the patients account and visit the Primary/Secondary/Patient tabs and remove anything that may be entered in the 'Country Code' field. From here the claim can be rebuilt and resent.
Valid Country Codes can be found at https://www.iso.org/obp/ui/#search.