- There are more servers than the license allows in 360 Monitoring
- The number of servers is supposed to be lower in general
The same server got added twice because of multiple agent installation attempts.
Note: For example, servers were added both via the Plesk UI and CLI.
Log in to Plesk 360
Go to Monitoring > Servers (next to Dashboard)
Click the "remove server" link under the inactive duplicated server (marked as "offline"):