What app/environments are you using. I do not know SimDashboard. Does ist support SimConnect events? (PLASMA_TOGGLE is a SimConnect event, not a variable.)
Some apps only support a restricted set of variables and events.
Edit: On the SimDashboard website there is a list of available events. “PLASMA TOGGLE” is not included. This is obvious as it is not a documented event. Try to convince the developer of SimDashboard to include it.