If you are trying to add SmartCite, but your Add-in button is grayed out, this means your IT department has to whitelist SmartCite because your organization is on a Microsoft Enterprise license.
Not to worry - it's an easy for your IT team to add and if they need additional information to do that, please contact us at firstname.lastname@example.org
In a nutshell, through the admin panel, your administrator can assign an add-in directly to a user, to multiple users via a group, or to everyone in the tenant. When the relevant Office application starts, the add-in automatically downloads for set of users your IT has permitted.
You can find step-by-step instructions here:
Once added, you will be able to find SmartCite either already pushed to your ribbon menu bar or if not, under "Admin Managed" tab in your Add-in menu.