com.facebook.sdk.core error 8

In my case this error was caused by improper bundle id set in facebook settings of the app itself. Facebook "bundle id" is case sensitive, in my Info.plist I had uppercase product name, but in fb settings - lowercase.

Make sure your permissions are typed correctly

   func loginButton(loginButton: FBSDKLoginButton!, didCompleteWithResult result: FBSDKLoginManagerLoginResult!, error: NSError!) {

            if error == nil {
                println("login complete")
                self.performSegueWithIdentifier("showLogin", sender: self)

            }else{

                println(error.localizedDescription)
    //com.facebook.sdk.core error 8.
            }
        }

In my case, I was using a Facebook account that hadn't yet been added to any of the Facebook app's admins/developers/testers roles.

In my case, after spending several hours of debugging I found that I was using the API,

func application(application: UIApplication,
                 openURL url: NSURL, options: [String: AnyObject]) -> Bool {
    if #available(iOS 9.0, *) {
        FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: options)
    } else {
        // Fallback on earlier versions
    }
    return true
}

which is deprecated for iOS 9.So, I used:

func application(application: UIApplication,
                 openURL url: NSURL, sourceApplication: String?, annotation: AnyObject) -> Bool {
    FBSDKApplicationDelegate.sharedInstance().application(application, openURL: url, sourceApplication: sourceApplication, annotation: annotation)
    return true
}

Which worked for me. Hope this saves time of someone.