This is a used Sennheiser Skm 100s G4 566-608 MHz handheld microphone with a e835 capsule.

It was working perfectly fine and somebody's synced to Mics to the same receiver.

Now I cannot get it to un-mute.

It will sink fine. But even with the pilot tone active or deactive I cannot get it to unmute and I have three other handhelds that sink fine so I don't need to keep playing with it. My last sugar game!