PHP curl API 调用失败，并显示 413

已经玩了一段时间了，这是一个连接到 API 的功能，UN/PW 和 URL 绝对是正确的。

但是，它一直失败并显示413错误代码，我理解这意味着到服务器的数据流太大，但我要做的就是连接尚未发送任何内容。

有什么建议吗？谢谢

function call_api () {
    $username = "***api un here***";
    $password = "***api pw here***";
    $url = "http://api.domain.com";
    $api_connect = curl_init(); 
    curl_setopt($api_connect, CURLOPT_URL, $url);   
    curl_setopt($api_connect, CURLOPT_USERPWD, "$username:$password");
    curl_setopt($api_connect, CURLOPT_CONNECTTIMEOUT, 30); 
    curl_setopt($api_connect, CURLOPT_TIMEOUT, 30); 
    curl_setopt($api_connect, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($api_connect, CURLOPT_POST, true); 
    curl_setopt($api_connect, CURLOPT_HEADER, 1); 
    $result = curl_exec($api_connect);
    $err = curl_error($api_connect);  
    if( curl_errno($api_connect) )
    {   
        $result = 'ERROR -> ' . curl_errno($api_connect) . ': ' . curl_error($api_connect);
    }
    else 
    {   
        $returnCode = (int)curl_getinfo($api_connect, CURLINFO_HTTP_CODE);              
        switch($returnCode)
        {      
            case 200: 
                 $result = 'HAVE CONNECTION -> ' . $returnCode; 
                 break;    
            default:     
                 $result = 'HTTP ERROR -> ' . $returnCode;        
                 break; 
        }
    }  
    curl_close($api_connect);
    echo $result;
}

更新

要添加到此

curl_errno($api_connect)返回 0

curl_error($api_connect)返回空字符串

print_r(curl_getinfo($api_connect)返回以下内容

Array
(
    [url] => https://api.domain.com
    [content_type] => text/html; charset=iso-8859-1
    [http_code] => 413
    [header_size] => 197
    [request_size] => 218
    [filetime] => -1
    [ssl_verify_result] => 0
    [redirect_count] => 0
    [total_time] => 0.065667
    [namelookup_time] => 0.001792
    [connect_time] => 0.010429
    [pretransfer_time] => 0.056323
    [size_upload] => 0
    [size_download] => 408
    [speed_download] => 6213
    [speed_upload] => 0
    [download_content_length] => -1
    [upload_content_length] => -1
    [starttransfer_time] => 0.065638
    [redirect_time] => 0
    [certinfo] => Array
        (
        )
    [redirect_url] => 
)