Instagram实时订阅活动日志

正在处理instgram实时订阅。我正在尝试根据订阅返回的对象id保存图像链接。活动日志仅捕获“N”，而不捕获图像链接。我做错了什么

<?php
if (isset ($_GET['hub_challenge'])){
    echo $_GET['hub_challenge'];
}
else{
    $myString = file_get_contents('php://input');
    $sub_update = json_decode($myString);
    $access_token = 'xxxxx';

     foreach($sub_update as $k => $v) // can be multiple updates per call
    {   $objid = $v->object_id;
        $recent_data = file_get_contents('https://api.instagram.com/v1/tags/'.$objid.'/media/recent?access_token='.$access_token);
        $results=$results['data'];
        $image_link = $results['images']['standard_resolution']['url'];
        file_put_contents('activity.log', serialize($image_link), FILE_APPEND | LOCK_EX);
    }
}
?>