The solution that onkar has posted did not work for me. I think that the Facebook app interface has changed since onkar's solution was posted.
Here is what worked for me:
1) Go to https://developers.facebook.com
2) From the top nav bar select: Apps >> Your App Name >> App Review
3) At the top of the Status & Review page you should see "Do you want to make this app and all its live features available to the general public?" with a toggle (no/yes) switch.
4) Click the toggle switch so it displays "Yes".
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