Basically, you need a list of all the user's friends on facebook to invite them. You can get a list of ALL friends only if your application is in the "GAMES" category.
If not, you can still get the user's friend list, but only some, not all. refer to the terms friends and invitable_friends on facebook.
So, here are a few things you can do (BUT NOT ALL IS RECOMMENDED)
Change your app’s category to “GAMES” and you can get a list of all your friends, and then you can use WebDialog and WebDialog.RequestsDialogBuilder to invite friends
specify any link to the canvas URL in the facebook application settings. this link will only be used when the user clicks your notification from the Internet. this link will not affect your application in any way.
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