Problems with API Zoho Subscriptions

Hello,

I am trying to get the list of customers with PHP, this is my script:

            $url = " https://subscriptions.zoho.com/api/v1/customers";

              $ch = curl_init();

            $header = array();
            $header[] = 'Content-Type: application/json;charset=UTF-8';
            $header[] = 'X-com-zoho-subscriptions-organizationid: '.$organization;
            $header[] = 'Authorization: Zoho-authtoken '.$token;

            curl_setopt($ch, CURLOPT_POST, 1);
              curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
            curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
              curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

              $Return = curl_exec($ch);
              curl_close($ch);

            echo $Return;

Any idea how I can get this to work?

Thanks,
Jorge