You need to set your app “live”.
Go to Status & Review tab in app dashboard, on top you find
“Do you want to make this app and all its live features available to the general public?”
… that one you need to set to Yes.
Before setting this to Yes, your app is considered to be in “development mode”, and therefor posts made via it are not shown to users that do not have a role in your app (admin/developer/tester).
