To update sublist data in existing records, instead of using a single import file that includes body field and sublist data, consider using a separate import file for the sublist data, in which you provide a reference to the record you want to update. This approach leads to improved performance.
Important
If you move a set of sublist data to a separate import file, you must do this with all other sublist data. In the following example, if you move Item and Quantity into a separate Item import file, you must also move Apply and Payment into a separate Apply import file.