Error:

Unable to list item.
The item specific Object Type is missing.
Add Object Type to this listing, enter a valid value, and then try again.

Reason:

Usually this is because the item needs to have an Object Type selected from Item Specifics.
This generally occurs with kitchen items such as cups, bowls, china etc.

Resolution:

Step 1: Go into the 'Edit' function and scroll down to item specifics and find Object Type
​Step 2: From here select the type of item this is

After selecting the correct Object Type for your item, you can resubmit this item and it will list properly.