Follow the steps below to connect a Plantronics CS540 headset to a Polycom phone.
Connect the APP51 cable
Connect the APP51 cable to the phone as indicated in the photo (if a headset is already present, be sure to unplug it completely).
Connect the APP51 cable to the base of the headset as indicated on the photo.
Connecting the power supply
Connect the power supply to the base of the headset in the intended location.
Put the headset to charge on the base for at least 20 minutes.
You should still have aside the cable provided with the helmet (photo below), it is normal.