Unable to added Facebook and Twitter to UIActivityViewController

Trying to share application on social median, and email, and message. Since Email and message is working fine for me. But Facebook,and twitter is not all showing to UIActivityViewController

Below is code which i try.

NSArray *excludeActivities = @[UIActivityTypeAirDrop,
                               UIActivityTypePostToFacebook,
                               UIActivityTypePostToTwitter];
UIActivityViewController *activityViewController =
[[UIActivityViewController alloc] initWithActivityItems:@[string, URL]
                                  applicationActivities:nil];
activityViewController.excludedActivityTypes = excludeActivities;
[self presentViewController:activityViewController
                                   animated:YES
                                 completion:^{
                                 }];

- (id)activityViewController:(UIActivityViewController *)activityViewController
         itemForActivityType:(NSString *)activityType
{
    if ([activityType isEqualToString:UIActivityTypePostToFacebook]) {
        return NSLocalizedString(@"calling facebook", );
    } else if ([activityType isEqualToString:UIActivityTypePostToTwitter]) {
        return NSLocalizedString(@"calling twitter", );
    } else {
        return nil;
    }
}

@All Please let me know what i need to do.