SOAP Client sending empty body Envelope

I can't find out where is the problem, I have prepared an XML for sending through the SOAP Client like so:

$client = new SoapClient($url, array(
    'trace' => true,
    "style"    => SOAP_RPC,
    "use"      => SOAP_ENCODED
));

$response = $client->sendItems($xml);

var_dump($client->__getLastRequest());

var_dump shows me string(233) " ", but when I'm testing it throught the PHPStorm Rest Client testing tool, it shows me this:

string(233) "<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://ift.tt/sVJIaE" xmlns:ns1="http://ift.tt/1KmkMQt"><SOAP-ENV:Body><ns1:sendItemsRequest/></SOAP-ENV:Body></SOAP-ENV:Envelope>
"

There are no content inside the body. I triple-checked that my $xml contains the full XML with bodycontent.

Anyone got similiar problem before or have some idea what's going on ?

==== UPDATED ====

Here is the XML Content:

<soapenv:Envelope xmlns:soapenv="http://ift.tt/sVJIaE" xmlns:ltm="http://ift.tt/1KmkMQt">
    <soapenv:Header/>
    <soapenv:Body>
        <ltm:sendItemsRequest>
            <ItemsToAdd>
                <ItemToAdd>
                    <description>DEMO DESCRIPTION text</description>
                    <url>http://localhost/media/items/0000000001.jpg</url>
                    <brand>BRANDTEST</brand>
                    <status>creation</status>
                    <statusDate>1423209737</statusDate>
                    <beginDate>1406844000</beginDate>
                    <endDate>1730329200</endDate>
                    <targets>
                            <barcode>1234567891011</barcode>
                            <barcode>9876543210123</barcode>
                    </targets>
                    <medias>
                        <media>
                            <retailer>RETAILERTEST</retailer>
                            <format>dummyformat</format>
                        </media>
                    </medias>
                </couponToAdd>
                </ItemToAdd>
        </ltm:sendCouponsRequest>
    </soapenv:Body>
</soapenv:Envelope>