Am I making the right request to follow on Twitter?

Question

PHP

With the help of this class I write following users. The code:

$settings = array(
    'oauth_access_token' => "blabla",
    'oauth_access_token_secret' => "blabla",
    'consumer_key' => "blabla",
    'consumer_secret' => "blabla"
);
$url = 'https://api.twitter.com/1.1/friendships/create.json'; 
$requestMethod = 'POST'; 
$twitter = new TwitterAPIExchange( $settings );

foreach($arUser as $name=>$info)
{
    $postField = '?screen_name='.$info->screen_name.'&user_id='.$info->id.'&follow=true';

    $follow = $twitter->setPostfields($postField)->buildOauth($url, $requestMethod)->performRequest();
}

The script is working, but nothing is returned in $follow, although there should be either an error or information about the screen_name user