Sorry for my late reply. I realised that we actually have a valid license for “Premium Addons Pro”, so I submitted a support ticket on your website and added the page URL and admin login details there.
It worked for me with these settings:
Dynamic Tag: Post Custom Field
Custom Key: “_stock_status”
Show/Hide: Hide when condition
Condition: “is equal to”
Conditional value: “outofstock”
Hope this helps!