Please check the commodity code for a Country using the following function or check the table T604 with country code ZA.
OLME --> Foreign trade/ Customs --> Basic data for foreign trade --> Define Commodity code / Import trade numbers by country
For better understanding, Please read the last section of the following link.
Foreign Trade Data in Purchasing Documents - Basic Functions (SD-FT-PRO) - SAP Library
You've to communicate with some screenshots in order to explain your need. For example, use the material master template where you'll assign the commodity code number. For details press F1.
