Invalid item reference key error in subsidiary

To resolve this error, check to see if the item being used as the free item on the promotions record have Display In Web Store = T. This is a requirement for all type of item especially for Non-Inventory items and/or Matrix Items

1. Navigate to Lists > Accounting > Items
2. Look for the item then click Edit
3. Click the Web Store tab
4. Locate the Display In Web Store field under the Web Store Display section
5. Check the Display In Web Store field
6. Click Save

Note: For Matrix Child Items, it is only required to check the Display In Web Store field for the child item itself. It is not required for the parent item.