How to duplicate a POST Request with CURL in PHP

Question

I have a webapp that needs to be able to recreate the post actions of application provided by our vendor. The application allows the user to log in or out of phone workgroups. I have captured the HTTP Post request that the application is sending to initiate a session and to log the user in and out of the workgroups. I would like to recreate these POSTs in PHP using CURL, but I am having some issues getting the POST correct.

The post I am trying to emulate as captured from WireShark looks like this :

POST /Login?timeout=6 HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: 10.1.##.##:5447
Content-Length: 160
Expect: 100-continue
Connection: Keep-Alive

{"username":"joell","user-auth-token":"TOKENTOKENTOKEN","user-role":"admin_role","client-type":3,"app-id":"cmwin.18.62.7800.0"}

Response

HTTP/1.1 200 OK
Content-Length: 58
Content-Type: text/plain; charset=UTF-8
Connection: Keep-Alive
Cache-Control: no-store
Date: Fri, 03 Apr 2015 13:08:42 GMT
Expires: Fri, 03 Apr 2015 13:08:42 GMT
Access-Control-Allow-Origin: *
Set-Cookie: SessionId=2006727099

My php code atempting to recreate this is:

$data = array(
            "username" => "joell",
            "user-auth-token" => "TOKENTOKENTOKEN",
            "user-role" => "admin_role",
            "client-type" => 3,
            "app-id" => "cmwin.18.62.7800.0"
            );                                                                    
    $data_string = json_encode($data);                                                                                   

    $curl = curl_init('http://10.1.##.##:5447/Login?timeout=6');                                                                      
    curl_setopt($curl, CURLOPT_CUSTOMREQUEST, "POST");                                                                     
    curl_setopt($curl, CURLOPT_POSTFIELDS, $data_string);                                                                  
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);                                                                      
    curl_setopt($curl, CURLOPT_HTTPHEADER, array(                                                                          
        'Content-Type: application/x-www-form-urlencoded',                                                                                
        'Content-Length: ' . strlen($data_string),
        'Expect: 100-continue',
        'Connection: Keep-Alive')                                                                       
    );   

    if(!curl_exec($curl)){
        die('Error: "' . curl_error($curl) . '" - Code: ' . curl_errno($curl));
    }
    $result = curl_exec($curl);
    print_r($result);
    curl_close($curl);

The request that my script is generating is:

POST /Login?timeout=6 HTTP/1.1
Host: 10.1.##.##:5447
Accept: */*
Content-Type: application/x-www-form-urlencoded
Content-Length: 160
Expect: 100-continue
Connection: Keep-Alive

{"username":"joell","user-auth-token":"TOKETOKETOKEN","user-role":"admin_role","client-type":3,"app-id":"cmwin.18.62.7800.0"}

Response

HTTP/1.1 200 OK
Content-Length: 20
Content-Type: text/plain; charset=UTF-8
Connection: Keep-Alive
Cache-Control: no-store
Date: Fri, 03 Apr 2015 15:15:44 GMT
Expires: Fri, 03 Apr 2015 15:15:44 GMT
Access-Control-Allow-Origin: *

Currently the output of my PHP script is :

{"error":2147483650}