You may see this error message inside Post Planner:
Facebook is rejecting our requests. Please logout of both Facebook and Post Planner, clear your cookies then comeback to retry your action.
The Fix
First thing you should do here is try the directions from the message (minus clearing browser cookies).
Logout of FB and Post Planner
Log back in and
If that doesn't work, do a full app reset.
If the full app reset doesn't fix the problem, something on your side is preventing Post Planner from extracting the necessary information from your profile.
This could be browser plugins, the browser itself, your Facebook settings, or actions taken by you which are blocking us.
In this case, please try with fresh browser and following all guidelines.