First off, you have to specify you wish to use Document Literal style:
$client = new SoapClient(NULL, array(
'location' => 'https://example.com/path/to/service',
'uri' => 'http://example.com/wsdl',
'trace' => 1,
'use' => SOAP_LITERAL)
);
Then, you need to transform your data into a SoapVar; I've written a simple transform function:
function soapify(array $data)
{
foreach ($data as &$value) {
if (is_array($value)) {
$value = soapify($value);
}
}
return new SoapVar($data, SOAP_ENC_OBJECT);
}
Then, you apply this transform function onto your data:
$data = soapify(array(
'Acquirer' => array(
'Id' => 'MyId',
'UserId' => 'MyUserId',
'Password' => 'MyPassword',
),
));
Finally, you call the service passing the Data parameter:
$method = 'Echo';
$result = $client->$method(new SoapParam($data, 'Data'));