PUT /categoria/{idCategoria}

curl    

curl -X POST "https://bling.com.br/Api/v2/categoria/{idCategoria}/json/"
     -d "apikey={apikey}"
     -d "xml={xml_da_categoria}"

PHP

$url = 'https://bling.com.br/Api/v2/categoria/{idCategoria}/json/';
$xml = '>...';
$posts = array (
    "apikey" => "{apikey}",
    "xml" => rawurlencode($xml)
);
$retorno = executeInsertCategory($url, $posts);
echo $retorno;
function executeInsertCategory($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;
}

C#

public static void ExecuteInsertCategory() {
    HttpWebRequest request =
        (HttpWebRequest)WebRequest.Create("https://bling.com.br/Api/v2/categoria/{idCategoria}/json/");
    ASCIIEncoding encoding = new ASCIIEncoding();
    string postData = "apikey={apiKey}&xml={xml_da_categoria}";
    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);
}