function do_https($url, $postfields) {
$login = "";
$pass = "";
$ch = curl_init($url);

// авторизация

curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_USERPWD, $login . ':' . $pass);

// на тесте необходимо отключить проверку подлинности сертификата "SSL certificate problem, verify that the CA cert is OK"

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

// результат вернуть в переменную

curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
if ($postfields)
{
  curl_setopt($ch, CURLOPT_POST, 1);
  curl_setopt($ch, CURLOPT_HTTPHEADER, Array("Content-Type:application/xml; charset=utf-8", "Content-Length:" . strlen($postfields)));
  curl_setopt($ch, CURLOPT_POSTFIELDS, $postfields);
}
$xmlString = curl_exec($ch);
$httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
$xml = simplexml_load_string($xmlString);
curl_close($ch);
return $xml;
}

$orderXML = new SimpleXMLElement($orderXMLString);

$orderXML->OrderNum = 'MyUnicumOrderNumber-1234567890';

$orderXML->PartNum = 'T5D-00432';

$orderXML->quantity = 1;

$postString = $orderXML->asXML();

$returnOrder = do_https("https://sandbox.webstore.mont.ru/B2BService.svc/web/AddOrder", $postString);

$orderXML = new SimpleXMLElement($orderXMLString);

$orderXML->OrderNum = 'MyUnicumOrderNumber-1234567890';

$postString = $orderXML->asXML();

$returnOrder = do_https("https://sandbox.webstore.mont.ru/B2BService.svc/web/GetOrder", $postString);

<TransactionOrderLine xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<OrderNum> MyUnicumOrderNumber-1234567890</OrderNum>

<DateOn>2020-01-29T16:34:46.04</DateOn>

<quantity>1</quantity>

<ProductId>22784a7b-d7d9-4e8b-9c35-2dd2b9632723</ProductId>

<Keys>

<ProductKey>

<ActiveKey>65451-51499-92851-19639-61472</ActiveKey>

<DateAdd>2020-01-29T16:34:47.9594557+04:00</DateAdd>

<VendorClientTransactionId>60a95697-2644-4f60-aca7-44c3933fb16f</VendorClientTransactionId>

<keyTypeId>3</keyTypeId>

<SequenceNumber>80107651820832040427</SequenceNumber>

<Description>Product activation code.</Description>

</ProductKey>

</Keys>

<Links>

<ProductLink> <Link>http://posa.vo.msecnd.net/db/Office2010_English_x32.exe?e=1354278887&h=48996ff787513b395b2b4022e73c4014</Link>

<DateAdd>2012-11-29T16:34:47.9674565+04:00</DateAdd>

<VendorClientTransactionId>60a95697-2644-4f60-aca7-44c3933fb16f</VendorClientTransactionId>

<linkTypeId>1</linkTypeId>

<Description>Download link for a 32 bit Microsoft software product (large setup file/s or ISO).</Description>

</ProductLink>

<ProductLink> <Link>http://posa.vo.msecnd.net/db/Office2010_English_x64.exe?e=1354278887&h=3eea8462ae94b8296bd548db2eda222b</Link>

<DateAdd>2012-11-29T16:34:47.9704568+04:00</DateAdd>

<VendorClientTransactionId>60a95697-2644-4f60-aca7-44c3933fb16f</VendorClientTransactionId>

<linkTypeId>1</linkTypeId>

<Description>Download link for a 64 bit Microsoft software product (large setup file/s or ISO).</Description>

</ProductLink>

</Links>
<Errors />

<Status>Завершен успешно</Status>

</TransactionOrderLine>