Soap Client Issue passing Param

I had a quick question about setting up a soap client

I am attempting to setup a SOAP client with a shipping company to get realtime tracking information.

Here is the function I have written for it:

def self.get_yellow_shipping_status(pro_number)

   XSD::Charset.encoding = 'UTF8'    tracking_number = "#{pro_number}"

   wsdl = "http://www.myyellow.com/dynamic/services/content/ecommerce/ etools/webservices/gtsimplfbn.wsdl"

   soap_client = SOAP::WSDLDriverFactory.new(wsdl).create_rpc_driver

    # Log SOAP request and response     @result = soap_client.getGenTrackingStatus("0475135680")     puts @result.inspect

   end

When I run the function I am able to return information from the yellow server, but I am getting an error code of 99. I have been in contact with the developers and they are saying that the PRONumber is not getting submitted to them. This number is the only parameter that this function expects. I manually added the pro # here "0475135680" and am at a loss for why it is not submitting the pronumber to the yellow soap server. Any hints or tips would be greatly appreciated.