Facebook requires acceptance of different terms of service depending on the type of custom audience you are trying to create.
While AdEspresso usually automatically does this for you, sometimes it is not possible.
If you're having troubles creating new custom audiences, first check that all the following links to Facebook's Terms of Service have been accepted. If not, please accept them and try again. Note they must be accepted by the same Facebook user who imported the ad account being used.
If you own a business manger account too, you also want to double-check this link: