Add Invoice# and PO# in FedEx Label in PHP

Question

I have integrated FedEx shipping services into my site. I am successful in creating the Shipping Label provided from FedEx, but the shipping label are missing values for some fields Like Invoice #, PO# and Reference # in the generated label.

I have passed values into request that is being made using soap request. The parameters are mentioned below :

$request['RequestedShipment'] = array(
                'CustomerReferences' => array(
                '0' => array(
                    'CustomerReferenceType' => 'P_O_NUMBER',
                    'Value' => 41111
                ),
               '1' => array(
                    'CustomerReferenceType' => 'INVOICE_NUMBER',
                    'Value' => 12345
                )
            )               
            );

The values are being passed into request. But the response does not return the same and the shipping label generated PDF. I have created FedEx library in Codeignitor and doing my work. Am I missing something or what I am unable to understand. I am generating this using developer details provided by FedEx. Any help will be grateful. Thanks in advance.