The add page selector only works if you have more than one free channel for static pages. The channel must be assigned as the type "Structure" under Modules » Structure » Settings and can not be used as a listing to show up within the menu.
Support
Having problems setting up and/or using Structure? Support is offered from 10am to 4pm EST weekdays. Send us an email at help@eeharbor.com and we will respond as quickly as we can.