This issue arises due to limitations associated with the PIN user configuration. This issue may occur even when logged in as an Admin. The root cause is that the Admin PIN has been changed from '0' to '1'. To resolve this issue:
Log out of UBS and log in as admin.
Go to Admin (at the right hand top right-hand), Administrator Settings, and User Management.
Choose the company and click User Account Roles.
Choose the userpin, edit, change the Pin to 0, and save.
Do the same for the inventory side.
Log out from UBS and log in again using your userpin, and the create button shall reappear.