The visibility for your posts must be set to Public to be able to publish on Facebook correctly.

It means that everyone will be able to see the posts, however, if the events or groups are private, only people that joined them will be able to see the posts.

To change the visibility all you have to do is:
 

  1. Login to Facebook
  2. Go to Settings 
  3. Select Apps 
  4. Look for Postcron and change the Visibility of App to Public.

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