For inviting friends to a group I use below code
Dim fb = New FacebookClient (TockenAccess)
Dim parameters As Object = New ExpandoObject ()
parameters.member = "1000048247037551"
Await fb.PostTaskAsync ("/ 1387586938758287 / members" parameters)
but they return the error.
An exception of type 'Facebook.FacebookOAuthException' occurred in mscorlib.dll but was not handled in user code
Additional information: (OAuthException - #3) (#3) Unknown method
error message : {"(OAuthException - #3) (#3) Unknown method"}