Bots (or any Webex Teams user) can only send messages from within rooms where they are a member, i.e. the bot will need to have been added to the room by another user, or be in a room in created. An extension of this involves Teams: users (and bots) that are members of a Team can list and join (and then send messages in) rooms that belong to Teams they are a member of.
So, only if all your rooms are under Teams, and your bot is a member of all Teams, can it be able to send messages into any room. Alternatively you would have to ensure the bot was a member of every room that could potentially need its services.