I'm having the same problem as this post, only the accepted answer doesn't work for me.
Sorry for re-posting the question, but I didn't if I can carry on a "me too" conversation in the answer thread?
When setting up a client's Member Group, I can't get Inventory to appear in the Store menu. I even duplicated the Super Admin's Member Group with all its privileges, but yet still couldn't get this to work. It seems that only {group_id==1} is able to see the Inventory tab.
This is an MSM site and even with the client's member group having access to all store-related channels in all sites, it's still a no-go...
EE 2.6.1, Store 1.6.4
Can access ADD-ONS section