> How are businesses going to get money if there are no humans that are able to pay for goods?

By transacting with other businesses. In theory comparative advantage will always ensure that some degree of trade takes place between completely automated enterprises and comparatively inefficient human labor; in practice the utility an AI could derive from these transactions might not be worth it for either party—the AI because the utility is so minimal, and the humans because the transactions cannot sustain their needs. This gets even more fraught if we assume an AGI takes control before cheaply available space flight, because at a certain point having insufficiently productive humans living on any area of sea or land becomes less efficient than replacing the humans with automatons (particularly when you account for the risk of their behaving in unexpected ways).