Voice
A call is for a customer who wants to talk the problem through, not type it. They press a button on your website, speak, and hear the assistant answer. You do not pick up the phone. The transcript still ends up in the inbox if a person needs to take over.
Dictation only fills the text field. Voice is the spoken conversation. They are separate switches. Turning one off leaves the other as it was. Both are the shop widget, not the inbox.
Why it spends more
A call processes audio for as long as it lasts, so it draws more credit than a typed thread. Usage shows that as Voice chat. Leave Call with the assistant off when you want customers to type. The chat button stays.
How to set it
In the group's Basic settings, under Voice on the website, turn on Call with the assistant. The customer needs a microphone. Only an admin can change this.
Voice the customer hears is which voice answers. Pick one and play the sample beside the list. The sample uses the group's language, so you hear it the way customers will. Save the one that fits the shop. You can change it later without turning the call off.