If your sidebar is turned on and you don't see in on your listings, it could be due to either:
Reason 1: Mobile Display
If you're viewing your listing design on mobile, some templates will hide the sidebar, or put it at the bottom.
Reason 2: Store Listing Frame
If you have an eBay Store subscription, eBay's default left sidebar may be forcing your design to hide your sidebar (not enough space).
To disable eBay's sidebar:
On the Listing Frames page, under Store Header Features,
choose either Store Header Only
After clicking Apply at the bottom of your screen, eBay's sidebar will be removed and your 3Dsellers sidebar will be displayed.