Create design for product at scalablepress API in PHP

$fields = array(
'type' =>'Case',
'name' =>'Samsung Galaxy S3 Case',
'sides' => array('front'=>array('colors'=>array('Gloss'),'sizes'=>array('width'=>5),'artwork'=>'absolute url of image','position'=>array('horizontal'=>'C','offset'=>array('top'=>'2.5'))))
);
//$postData = http_build_query($fields);
$postData = json_encode($fields);

$url = 'https://api.scalablepress.com/v2/design';
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL, $url);
curl_setopt($ch,CURLOPT_POST ,true);
curl_setopt($ch,CURLOPT_SSL_VERIFYPEER ,0);
curl_setopt($ch,CURLOPT_HEADER, 1);
curl_setopt($ch,CURLOPT_HTTPHEADER, array('Content-type:application/json'));
curl_setopt($ch,CURLOPT_USERPWD, 'u:40238020c4ee790c2c159a58b5b30dae');
curl_setopt($ch,CURLOPT_POSTFIELDS, $postData);
if(curl_exec($ch) === false)
{
echo 'Curl error: ' . curl_error($ch);
} else
{


}