Json Code Validation Error Curl Post Request

I am getting following JSON output using curl in PHP

CURL:

$request = curl_init("{$config['root']}/api/tickets");
    curl_setopt($request, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($request, CURLOPT_POST, true);
    curl_setopt($request, CURLOPT_POSTFIELDS, json_encode($body));
    curl_setopt($request, CURLOPT_TIMEOUT, 30);
    add_headers($request);    
    $response = curl_exec($request);

Function:

function add_headers($request) {
    global $config;
    $headers = array('Content-Type: application/json');
    if (empty($config['accessClient'])) {
        curl_setopt($request, CURLOPT_USERPWD, "{$config['user']}:{$config['password']}");
    } else {
        array_push($headers, "Access-Client-Token: {$config['accessClient']}");
    }
    curl_setopt($request, CURLOPT_HTTPHEADER, $headers);
}

Output:

"{"amount":"100","description":"A ticket of 100.","payer":null,"successUrl":"http:\/\/localhost\/wordpress5\/ticket-confirmed.php","successWebhook":"http:\/\/localhost\/wordpress5\/ticket-confirmed-webhook.php","cancelUrl":"http:\/\/localhost\/wordpress5\/shop","orderId":"OID-1","expiresAfter":{"amount":1,"field":"hours"},"customValues":{}}"

and curl response is "

"{"Code":"Validation"}"

Developer Console:

Malformed JSON Ouput

Note: Values got from NetBeans Variables.

from Json Code Validation Error Curl Post Request