App not setup: This app is still in development mode

STEP 1:

In Settings -> Basic -> Contact Email. (Give your/any email)

STEP 2:in 'App Review' Tab : change

Do you want to make this app and all its live features available to the general public? Yes

And cheers ..

make sure your app is live on developer.facebook.com

This green circle is indicating the app is live

If it is not then follow this two steps for make your app live

Step 1 Go to your application -> setting => and add Contact Email and apply save Changes

Setp 2 Then goto App Review option and make sure this toggle is Yes i added a screen shot

This is an answer I haven't seen much around (this it was in a comment somewhere) although yes taking the app off development mode will work this can be bad for security or really annoying if the app isn't ready yet but you need to submit the app for review on account of needing access to special permissions (e.g. user_birthday).

What I did instead to fix the error was go to https://developers.facebook.com/sa/apps/{appId}/roles/ or from the app dashboard click roles on the left side

Then add the user account(s) to either developer or tester. Developers will need to be verified by mobile and will get access to the app to make changes but a tester will only need to be verified by email (not sure if even this is necessary but it probably is) and will only be able to use the API instead of make changes to settings.

If the app is ready for the public, obviously just take the app off development mode.