Sometimes, Facebook will show an "unexpected" or "unknown" error when trying to perform any action.
This is usually caused by an issue on Facebook's side and clears up after a few minutes. But sometimes Facebook will need you to clear cache to reset.
Common Error Messages
An unexpected error has occurred. Please retry your request later
An unknown error has occurred
The Fix
Clear your cache!
The keyboard shortcut to this is CMD/CTRL + SHIFT + DELETE
For Chrome, here's how to it looks:
Once you click "Clear data" and clear your browser cache, close and re-open your browser. Then launch Facebook and login.
Then open another tab on the same browser, and login to Post Planner:
New app here: https://app.postplanner.com/login
Classic app here: https://love.postplanner.com/login/
If you continue to experience the error, please do a full app reset.