How to enable eBay custom label/SKU# field

In Selling Manager and Selling Manager Pro, the Custom Label field lets you create product identifiers or SKUs to track and manage your inventory. You can enter up to 50 characters to identify the product how you want. The Custom Label will appear in place of the Part Number field. However, if you have information in the Part Number field it will be moved to the Custom Label field. You will be able to view, sort, and report by this field.

By default custom label is hidden. To enable custom label go to your eBay selling manager, click on the Customize link at top right corner.
A dialog will pop up as shown.
Check the checkbox before Custom label and adjust the order in Arrange columns.
Click Apply button to close the dialog.
You will see a new column in your item list as shown.