php soapclient wsdl SOAP-ERROR: Parsing WSDL: Couldn't load from

It often happens that providers neglect their SSL certificates and hence the sites and services end up having an invalid certificates - I suspect this is the case here.

Disabling the certificate validation as described by Kaii here or even better get your provider to fix their certificate.

Your code could/should then be something like:

$url     = "https://sampleurl.com/MerchantQueryService.asmx?WSDL ";
$context = stream_context_create(array(
        'ssl' => array(
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
        )
));

$rq = ["userName" => "username_here",
       "passWord" => "password_here",
       "referenceId" => "3455566694",
       "msisdn" => "346774313"];

$service = new SoapClient($url, array('stream_context' => $context));
$service->RequestTransaction($rq);