The following error appears on attempts to activate 360 Monitoring from the Plesk UI:
An error has occurred when trying to open the server monitoring confirmation page
The server does not exist in Server Inventory
The connection from the Plesk server to Plesk 360 exists just on the Plesk server.
Note: Before a Plesk server is added to 360 Monitoring, it has to be added to the Server Inventory of this account.