Controlio licenses apply for concurrent user sessions. Usually, user sessions are equal to the number of PCs.
But in some cases, the 'client limit exceeded' message may appear if you use 2 user sessions on 1 PC at the same time (2 users are signed in).
Please sign out from any extra Windows/macOS session(s) or send a request to add a license.
If needed, you can always free a license, and use it on the computer of choice.