If you have changed your Facebook password recently, you may have trouble posting your photos and will receive an error that says: : 'post' error:  Error validating access token: Session does not match current stored session. This may be because the user changed the password since the time the session was created or Facebook has changed the session for security reasons.
When you do this, it will change the permissions that POP has to post or delete for you. To fix your permissions, you will want to do the Nuclear Option: https://support.popitup.com/support/solutions/articles/16000062451-nuclear-option-pop. Once you set your permissions again, you should be able to post and make requests through POP again.