SOAP function giving me a 500 error - php

Question

I'm trying to connect to a soap api, but every time i try and call a function i get a 500 internal error.
I able able to call $client->__getFunctions() with out any issue, so i'm guessing that the code was able to connect to the soap server ok? I can see the function that i'm trying to call in the array:
GetCatalogFullResponse GetCatalogFull(GetCatalogFull $parameters)
heres my code:
$GUID = '000-000-000-000';
$user = 'user';
$pass = 'pass';
$url = 'https://example.net/webservices.asmx?WSDL';
$localCert = "cert.pem";
$options = array(
'local_cert' => $localCert,
'user' => $user,
'passphrase' =>$pass,
'soap_version' => SOAP_1_2,
);
try {
$client = new SoapClient($url, $options);
$result = $client->GetCatalogFull(['AccountGUID'=>$GUID,'UserLogin'=>$user]);
echo '<pre>';
print_r($client->__getFunctions());
} catch (SoapFault $fault) {
trigger_error("SOAP Fault: (faultcode: {$fault->faultcode}, faultstring: {$fault->faultstring})", E_USER_ERROR);
}
this is the request i am trying to make with the soap client class:
<?xml version="1.0" encoding="utf-8"?>
<soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">
<soap12:Body>
<GetCatalogFull xmlns="http://www.example.com">
<AccountGUID>string</AccountGUID>
<UserLogin>string</UserLogin>
</GetCatalogFull>
</soap12:Body>
</soap12:Envelope>