Starting with Version 3.0 just:in Engines (mac or linux) can be activated for live:cut. just:in Engine activation keys have to be requested for this to work. Refer to the chapter Activation to learn how to request and enter an activation key. If the just:in engine (either just:in Mac or Linux) is not activated for live:cut, just:control can not switch into live:cut mode.
The Activation Tab can be found within the just:control Configuration Panel.