This probably means that the installation procedure was not followed. To fix this issue, you must first check your add-ins:
Check my add-ins on Outlook:
To do this, you can click on the "..." then "Get Add-ins". If this is complicated, you can also follow this link which will open the add-ins window in your browser:
Web version:

Application:

Then you can click on My add-ins:
If your installation is correct, then the Add-in should be found in "Managed by the administrator"
Correct installation:

Incorrect Installation:

You will need to remove the add-in and then wait for the add-in to redeploy correctly.

If your problem persists, do not hesitate to contact support via live chat.