Make sure the LED works as designed. If you press the membrane switch, you should see the LED above the pin illuminate in Conference Composer as well as on the MX392. Since the switch is a toggle switch, the LED will stay lit until the switch is pushed again:
When the membrane switch is pushed again, the Vortex Device toggles the state from unmuted to muted. Now, the LED should not be illuminated since the input from the MX392 is now muted. Both LED's (Conference Composer and MX392) should not be illuminated:
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