@HoracioS
It can be the case that you have some license related issues.
Try to do the following:
a) go to "Tools & Settings > Plesk > License Management (click) > Additional License Keys (Tab)"
b) check that you have a key-name "unity-mobile-unix":
- if not, your Power Pack license has to be re-installed,
- if yes, verify that the key-number starts with EXT (followed by some digits)
and if the key-number for key-name "unity-mobile-unix" is starting with APS (followed by some digits), proceed with step c,
c) go to the tab "Plesk License key" and click "Retrieve keys".
That should do the trick.
Note that the likely root cause of the problem is that the license for Unity has expired and that the Plesk instance was not able to update the license keys.
If the latter is the case, you should also have received a number of error notifications by mail with the topic "Plesk key update deferral notification".
Anyway, hope the above helps!
Regards....