The error (Ship Web Service Error Message: An exception has been raised as a result of client data. InnerMessage: Hard128102 Invalid or missing sold to country code) from UPS typically occurs when the country selected for the order is either invalid or missing its ISO country code.
To resolve this issue please review the steps below:
Click Settings then Countries.
Search for the relevant country.
Ensure that both the Code (ISO 2-letter) and Code3 (ISO 3-letter) fields are correctly populated.
Click Edit and ensure there are no leading/ trailing spaces in the fields.
By following these steps, you should be able to resolve the error.