powl - how to attach invoice header level attachment in powl column field

hi,

I have a powl to display invoice, SRM.

Now I need to attach header level attachment of each invoice - as an column - say 'ATTACH'.

I took it as 'LA' in field-cat.

Now in Handle Action -->

when 'ATTACH'

lo_window = lo_window_manager->create_external_window(

       title          = 'ATTACH'

       url            = http://srd-abap.ltc.com:8004/sap/ebp/docserver?phioget&KpId=005056B363

       modal          = abap_false

       has_menubar    = abap_false

       is_resizable   = abap_true

       has_scrollbars = abap_true

       has_statusbar  = abap_false

       has_toolbar    = abap_false ).

But its not working, I think create external window is only for webdyn & not for POWL.

Can you give me any idea ???