POST /notaservico

$url = 'https://www.bling.com.br/Api/v2/notaservico/json/';
$xml = '<?xml version="1.0" encoding="UTF-8"?><pedido>...</pedido>';
$posts = array (
    "apikey" => "{apikey}",
    "xml" => rawurlencode($xml)
);
$retorno = execute($url, $posts);
echo $retorno;
function execute($url, $data){
    $curl_handle = curl_init();
    curl_setopt($curl_handle, CURLOPT_URL, $url);
    curl_setopt($curl_handle, CURLOPT_POST, count($data));
    curl_setopt($curl_handle, CURLOPT_POSTFIELDS, $data);
    curl_setopt($curl_handle, CURLOPT_RETURNTRANSFER, TRUE);
    $response = curl_exec($curl_handle);
    curl_close($curl_handle);
    return $response;
}

public static void Execute() {
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://www.bling.com.br/Api/v2/notaservico/");
    ASCIIEncoding encoding = new ASCIIEncoding();
    string postData = "apikey={apikey}&xml={xml_da_nota}";
    byte[] data = encoding.GetBytes(postData);
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    request.ContentLength = data.Length;
    using (Stream stream = request.GetRequestStream())
    stream.Write(data,0,data.Length);
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
    Console.Out.WriteLine("Response Body: \r\n {0}", responseString);
}