If you are using Current Works Sidkeys (USB) transmitters, click the drop-down and select Current Works Sidkeys:
Note: You do NOT indicate which Leader Transmitter is facilitating the game. After selecting Current Works Sidekeys as your transmitter system, AllPlay automatically knows which transmitter to designate as the Host/Leader Transmitter.
HINT: Make sure the red LED light on the USB receiver is set to: "AllPlay/Question Bowl" or "AllPlay/Question Bowl/GSP4".