I have FB App and through it created group, so I can invite/add new members of this group (via Facebook Graph API). It works perfect 4 days ago, but now I get error
"(#3) Application must be whitelisted or users must be testers."
and I can't add new member again. I can't find anywhere what's a "whitelist" and how to add my App on it. Can anyone advise me?
Your application must be in development mode, so you cannot send invitations to the users other than administrators/testers/developers of the application.
So either make your app live-
Or, if you don't want to make the app live for now, add some more testers whom you can send the invites-
Edit:
Also check if your app is published in App Center as a game or not? In that case the documentation says-