CURL XML почтовый запрос

Question

Кажется, что у меня проблема, когда я пытаюсь отправить запрос на сервер в php.HTTP-запрос API выглядит примерно так:

// XML
$xml_string = '<?xml version=\"1.0\" encoding=\"UTF-8\"?><PriceAvailabilityRequest><Header><MessageId>MSG-2018-12-10T10:18:07+0900</MessageId><Timestamp>2018-12-10T10:18:07+0900</Timestamp></Header><RequesterInfo><Customer code=\"APIKEY\"/><Location code=\"\"/><PreferredLanguage>EN</PreferredLanguage><PreferredCountry>DE</PreferredCountry></RequesterInfo><ProductRequest><SupplierPartNumber>00010-100G</SupplierPartNumber><UnitOfMeasure unit=\"EA\"/><Quantity>1</Quantity></ProductRequest></PriceAvailabilityRequest>';
// REST API URL
$url = 'https://webqws.sial.com/b2b?msgFmt=PriceAvailabilityRequest';
// header info
$headers = array(
    "Content-type: text/xml;charset=\"utf-8\"",
    "Accept: text/xml",
    "Cache-Control: no-cache",
    "Pragma: no-cache",
    "SOAPAction: \"run\""
);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, 1);

// send xml request to a server

curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt ($ch, CURLOPT_SSL_VERIFYPEER, 0);

curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)');

curl_setopt($ch, CURLOPT_POSTFIELDS,  $xml_string);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

curl_setopt($ch, CURLOPT_VERBOSE, 0);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$data = curl_exec($ch);
$data = simplexml_load_string(stripslashes($data));  
$info = curl_getinfo($ch);
curl_close($ch);

Это то, что я получаю из оператора print_r (curl_getinfo ($ ch)):

Array
(
    [url] => https://webqws.sial.com/b2b?msgFmt=PriceAvailabilityRequest
    [content_type] => text/xml;charset="utf-8"
    [http_code] => 400
    [header_size] => 1963
    [request_size] => 323
    [filetime] => -1
    [ssl_verify_result] => 0
    [redirect_count] => 0
    [total_time] => 0.558302
    [namelookup_time] => 0.266533
    [connect_time] => 0.268885
    [pretransfer_time] => 0.286032
    [size_upload] => 508
    [size_download] => 508
    [speed_download] => 910
    [speed_upload] => 910
    [download_content_length] => 508
    [upload_content_length] => 508
    [starttransfer_time] => 0.286037
    [redirect_time] => 0
    [redirect_url] => 
    [primary_ip] => 184.25.83.215
    [certinfo] => Array
        (
        )

    [primary_port] => 443
    [local_ip] => 223.26.138.3
    [local_port] => 48054
)

Я не уверен, чторешение может быть, и я некоторое время смотрю на эту проблему, надеюсь, кто-то может мне помочь, спасибо:)