CSV Import Assembly Item error: Please select member items before submitting

When Member Items are created in a separate CSV file there needs to be a linking column:
-Assembly Item: External ID, Internal ID or Name

Steps to do the import:

1. Navigate to Setup > Import/Export > Import CSV Records

2. Import Type = Item

3. Record Type = Assembly/BOM Item

4. Select Multiple files to upload
     Select file with Assembly Item for Primary File - Item
    Select file with member items for Linked File (Optional) - Item Members

5. Click Next

6. Set Primary File Key Column = (match the column set for link)

7. Click Next

8. Set Data Handling = Add
9. Click Next

10. Mapping of columns:

    Map all Assembly Item fields with fields from the Item folder
    Map the member items name and quantity with Item (Req) and Quantity in the Item Members folder
11. Click Next

12. Type the Import Map Name

13. Click Save & Run