Fetch Product Attributes using get_extension

Hello TechGurus,

I am executing BOL Query 'IsuOrderItemQuery' by passing 'CA_number' which is giving me list of ISU Contracts. Now for each contract's product , I need to fetch product attributes (Custom).

I am trying to fetch the same using class method cl_crm_isu_order_info=>get_extension. I am passing item GUID to this method along with attribute name as a object name but I am failed to fetch the value of the attribute.

I am using below code.

    cl_crm_isu_order_info=>get_extension( EXPORTING iv_guid        = l_wa_ser_contr-guid "contains item guid
                                                iv_object_name = 'ZDEVICE_CR_PP'
                                      CHANGING  ct_extension   = <it_extension> ).

What may be the reason behind this? Any pointers towards this will be appreciated

Thanks in Advance,

Prashant