You can use this parameter to enable the HTTP/WSS remote control API for VDO.Ninja. You pass a API KEY value to the parameter, and if it matches the remote control's API KEY, then the remote control interface will be able to send commands to your VDO.Ninja session.
You can control guests in the director's room, or you can control your local microphone and camera, as examples.
Please see https://github.com/steveseguin/Companion-Ninja for documentation and details of this command.
Please see https://companion.vdo.ninja for a sample interface to test this command out with.