Parse Sign In With Facebook Doesn't Work

#import "FBLoginViewController.h"

@interface FBLoginViewController () <CommsDelegate>
@property (nonatomic, strong) IBOutlet UIButton *btnLogin;
@property (nonatomic, strong) IBOutlet UIActivityIndicatorView *activityLogin;
@end

@implementation FBLoginViewController



- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

    }
    return self;
}

- (void) viewDidLoad
{
    [super viewDidLoad];
    [self.navigationController setNavigationBarHidden:YES];



    // Ensure the User is Logged out when loading this View Controller
    // Going forward, we would check the state of the current user and bypass the Login Screen
    // but here, the Login screen is an important part of the tutorial
    [PFUser logOut];
}

// Outlet for FBLogin button
- (IBAction) loginPressed:(id)sender
{
    // Disable the Login button to prevent multiple touches
    [_btnLogin setEnabled:NO];

    // Show an activity indicator
    [_activityLogin startAnimating];

    // Do the login
    [Comms login:self];
}


- (void) commsDidLogin:(BOOL)loggedIn {
    // Re-enable the Login button
    [_btnLogin setEnabled:YES];

    // Stop the activity indicator
    [_activityLogin stopAnimating];

    // Did we login successfully ?
    if (loggedIn) {
        // Seque to the Image Wall
        [self performSegueWithIdentifier:@"LoginSuccessful" sender:self];
    } else {
        // Show error alert
        [[[UIAlertView alloc] initWithTitle:@"Error"
                                    message:@"Registration failed. Please try again"
                                   delegate:nil
                          cancelButtonTitle:@"Okay"
                          otherButtonTitles:nil] show];
    }
}

@end