Upload file with Box.com PHP API

I am trying to upload a file to box.com using Box API. According to the docs, the curl request has to look like this: ``` curl https://upload.box.com/api/2.0/files/content \ -H "Authorization: Bearer ACCESS_TOKEN" -X POST \ -F attributes='{"name":nameOftheFile, "parent":{"id":parentId}}' \ -F file=@file ``` Here's what I did: ``` $token = "......"; $url = https://upload.box.com/api/2.0/files/content; $file_upload; foreach ($_FILES['file']['name'] as $position => $file) { $file_upload = $_FILES['file']['tmp_name'][$position]; } $json = json_encode(array('name' => $file ,array('parent' => array('id' => 0)))); $attrs = array('attributes' => $json,'file'=>'@'.$file_upload); $this->post($url,($attrs)); // Post function function post($url,$fields){ try { $ch = curl_init(); curl_setopt($ch,CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_HTTPHEADER, array( 'Authorization: Bearer '.$this->token )); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_POSTFIELDS, $fields); self::$response = curl_exec($ch); curl_close($ch); } catch (Exception $e) { self::$response = $e->getMessage(); } return self::$response; } ``` But it doesn't work. Is there anything wrong in curl part?