The license determines the amount of cameras that can be added. Ksenos allows adding an unlimited amount of cameras, but after the license runs out, the camera will show an Insufficient license text at the top of the settings.
A camera reserves a license even if it's an empty camera with no connection or signal, and without any IP address or credentials given. If a camera is broken and does not exist anymore, it can be disabled from the camera's settings from General > Camera > Disable this camera.
A camera can also be removed from the settings to allow the license for a new one. Right-click on the camera name from Menu > Settings > Cameras to get a menu with the Remove option or select the camera and click on the icon.