The intercom is the communication tool between the producer and the different camera operators. Its execution takes place through the Watchity APP and the Live Mixer. The producer is supposed to be able to issue and receive voice commands (talk and listen), while operators can only receive (listen). Otherwise, the operator's voice would enter as part of the input audio of that contribution.
In the configuration of your Direct of the type 'Professional Production', you must add the different users who will receive the instructions from the producer in the Live Mixer. Keep in mind that you can only add Intercom users that you have assigned as responsible for a mobile contribution created. That users, also, must be part of your workspace (as administrators or as editors).