$url = "print.php";

$dados = array(
    "urlReturn" => $urlReturn,
    "numberOrder" => $numberOrder,
    "hashstring" => $hashstring,
    "amount" => $amount
);

$string_campos = "";
foreach ($dados as $name => $valor) {
    $string_campos .= $name . "=" . $valor . "&";
}
$string_campos = rtrim($string_campos."&");
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch,CURLOPT_POST,count($dados));
curl_setopt($ch,CURLOPT_POSTFIELDS,$string_campos);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_exec($ch);
curl_close($ch);