Facebook Pages - Facebook Business Page - Authenticate Account - Pages
You must be logged into account that contains the pages where you want to post your socialcast.
For Example: If your business page is connected to your personal profile, authenticate with your personal login information.
Click the check box next to the right of the social site Facebook. Now select Load Pages from the Facebook drop down list to bring up any pages associated with your login.
You should see your Business Page from your drop list.