Mismatch Result: Soap Call - PHP

I've been working with the soap client in php and I've successfully been able to make a couple of soap calls to remote servers. These were done with tutorials and so many of the steps were laid out for me. Right now, however, I am trying to send a soap call to another server at

http://ift.tt/1n3nlZx I'm using SoapUI which allows me to see the xml of a correct request. Which I will post below.

    <soapenv:Envelope xmlns:xsi="http://ift.tt/ra1lAU" xmlns:xsd="http://ift.tt/tphNwY" xmlns:soapenv="http://ift.tt/sVJIaE" xmlns:soap="http://ift.tt/1n3nmfL">
   <soapenv:Header/>
   <soapenv:Body>
      <soap:Method1 soapenv:encodingStyle="http://ift.tt/wEYywg">
         <bstrParam1 xsi:type="xsd:string">Hello</bstrParam1>
         <bstrParam2 xsi:type="xsd:string">World</bstrParam2>
      </soap:Method1>
   </soapenv:Body>
</soapenv:Envelope>

When this soap call is sent it returns "Your input parameters are Hello and World".

Now, however, I am trying to convert what I did via xml into php. I've written

    $wsdl = "http://ift.tt/1n3nlZx";

$client = new SoapClient($wsdl, array(
                            "trace"=>1,
                            "exceptions"=>0));
$parameters = array('bstrParam1'=>'Hello', 'bstrParam2'=>'World');

$return = $client->Method1($parameters);

This however returns something nasty: SoapFaultObject type: Mismatch

Am I misreading the xml file that SoapUI gave to me? How could I convert the xml file above (which I know works) into php?