If you're struggling to add your Facebook Page or Group to Post Planner, begin by clicking the gear icon (Settings) and then navigating to, "Social Networks."
This is where you'll see the icons of all Facebook Pages or Groups you administer. Anything highlighted has been authorized for posting while gray icons are currently inactive.
To activate a specific Page or Group, hover over the icon and click on it.
If you don't see an icon for a particular Page or Group, you'll need to re-authorize the app through your Facebook profile. To do this, click on the "Refresh" button next to Facebook under, Settings - Social Networks.
Once refreshed, you should see that Page or Profile included in your list.
If you're not an administrator for a Page or Group (you only have a Member / Editor / Manager role), you will not be able to post via Post Planner until your rights have been upgraded by the Administrator of the Page or Group.