授权请求出现问题

我正在尝试在 Sinch 服务中发出conferenceCallout 请求，但我在签名方面遇到问题。我粘贴代码：

<?php 
//JSon Object
$conferencia['method']="conferenceCallout";
$participante['cli']="46000000000";
$destination['type']="username";
$destination['endpoint']="roke1";
$participante['destination']=$destination;
$participante['domain']="mxp";
$participante['custom']="customData";
$participante['locale']="en-US";
$participante['greeting']="Welcome to my conference";
$participante['conferenceId']="conferencia_de_prueba";
$participante["enableDice"]=false;

$conferencia['conferenceCallout']=$participante;

$data=json_encode($conferencia);



$md5_body = base64_encode ( MD5 ( utf8_encode ( json_encode($conferencia) ) ) );

$applicationKey="XXXXXX-xXXX-XXXX-XXXX-XXXXXXXX";
$applicationSecret="XXXXXXXXXXXXXXXX==";

$timestamp = new DateTime('NOW');

$StringToSign ="POST
        ".$md5_body."
        application/json
        x-timestamp:".$timestamp->format(DateTime::ISO8601)."
        /v1/callouts";

$utf8encode=utf8_encode($StringToSign);
$hash= hash_hmac("sha256",$applicationSecret,$utf8encode);
$base64=base64_encode($hash);

$Signature =$base64;
$Autorization = "Application"." ".$applicationKey.":".$Signature;


$ch = curl_init('https://callingapi.sinch.com/v1/callouts');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS,$data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'Content-Type: application/json',
        'Authorization:' . $Autorization,
        'X-Timestamp: ' . $timestamp->format(DateTime::ISO8601),
        'Content-Length: ' . strlen($data))
        );

$result = curl_exec($ch);
echo $result;

?>

但我收到错误代码 40102，即 40102 - 签名无效。

谁能帮我？我做错了什么？

此致。

我发布了对我有用的代码。

$phone ="+460000000" //Put the destination number here
$key = "XXXXXX";    
$secret = "XXXXXX"; 
$message = $first_name . ', thanks you for signing in. We will text you when we\'re ready for you';
$phone   = $phone_number;

$body = json_encode(array('From' => $rented_number, 'Message'=>$message, ));

$timestamp = date("c");

$path                  = "/v1/sms".$phone;
$content_type          = "application/json";
$canonicalized_headers = "x-timestamp:" . $timestamp;

$content_md5 = base64_encode( md5( utf8_encode($body), true ));

$string_to_sign =
    "POST\n".
    $content_md5."\n".
    $content_type."\n".
    $canonicalized_headers."\n".
    $path;

$signature = base64_encode(hash_hmac("sha256", utf8_encode($string_to_sign), base64_decode($secret), true));
$authorization = "Application " . $key . ":" . $signature;

$service_url = 'https://messagingapi.sinch.com'.$path;
$curl = curl_init($service_url);
curl_setopt($curl, CURLOPT_HTTPHEADER, array(
    'content-type: '.$content_type,
    'x-timestamp:' . $timestamp,
    'authorization:' . $authorization
));
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $body);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
$curl_response = curl_exec($curl);
// @todo: checking response / working with results
curl_close($curl);

感谢draw010 的帮助，太棒了！