使用 AcrCloud RESTful api php 上传音频文件时出现500错误

我正在使用php上传音频文件，但是出现以下错误: 我在Postman中尝试了相同的凭据，它可以工作。 我找不到错误在哪里

我遵循ACRCloud文档[这里]（https://github.com/acrcloud/webapi_example/blob/master/RESTful%20service/upload_audios.php）

 HTTP/1.1 100 Continue
    < HTTP/1.1 500 Internal Server Error
    < Server: openresty/1.9.7.4
    < Date: Mon, 23 Jan 2017 16:51:29 GMT
    < Content-Type: application/json; charset=UTF-8
    < Transfer-Encoding: chunked
    < Connection: keep-alive
    < X-Powered-By: PHP/5.6.21
    < X-Rate-Limit-Limit: 600
    < X-Rate-Limit-Remaining: 599
    < X-Rate-Limit-Reset: 0

    发送完成前的HTTP错误，停止发送
    <
    关闭连接0`

我的代码

$request_url = 'https://api.acrcloud.com/v1/audios';
$http_method = 'POST';
$http_uri = '/v1/audios';
$timestamp = time();
$signature_version = '1';
$account_access_key = '';
$account_access_secret = '';
$string_to_sign =
$http_method . "\n" .
$http_uri . "\n" .
$account_access_key . "\n" .
$signature_version . "\n" .
$timestamp;
$signature = base64_encode(hash_hmac("sha1", $string_to_sign, $account_access_secret, true));
$realpath = realpath('uploads/*****.mp3');

    if(class_exists('\CURLFile'))
        $cfile = new \CURLFile($realpath, "audio/mp3", basename($realpath));
    else
        $cfile = '@' . $realpath;
    $fields = array(
        'audio_id' => '30007',
        'title' => 'aya number 19',
        'audio_file' => $cfile,
        'bucket_name' => 'whatever',
        'data_type' => 'audio',  // 如果上传的是指纹文件，请设置 'data_type'=>'fingerprint'
        'custom_key[0]' => 'track_id',
    );
    $headerArray = array();
    $headers = array(
        'access-key' => $account_access_key,
        'signature' => $signature,
        'signature-version' => '1',
        'timestamp' => $timestamp,
    );
    foreach( $headers as $n => $v ) {
        $headerArr[] = $n .':' . $v;
    }
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $request_url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_VERBOSE, true);
    $verbose = fopen('php://temp', 'w+');
    curl_setopt($ch, CURLOPT_STDERR, $verbose);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headerArr);
    $result = curl_exec($ch);
    if ($result === FALSE) {
        printf("cUrl error (#%d): %s<br>\n", curl_errno($ch),
            htmlspecialchars(curl_error($ch)));
    }
    rewind($verbose);
    $verboseLog = stream_get_contents($verbose);

    echo "详细信息:\n<pre>", htmlspecialchars($verboseLog), "</pre>\n";
    dd($result);
    curl_close($ch);