FM BBP_PD_PO_UPDATE is not updating Purchase Order

Hi Experts,

I am trying to update Final Delivery and Final Invoice indicator for a PO using FM BBP_PD_PO_UPDATE.

Code Snippet for FM call is as follows: -

      CALL FUNCTION 'BBP_PD_PO_UPDATE'
        EXPORTING
          i_header                = wa_po_header1
          i_save                  = 'X'
          iv_with_change_approval = 'X'
        IMPORTING
          es_header               = wa_po_hdr_upd
        TABLES
          i_item                  = it_po_item1
          e_messages              = it_po_message.

Here all the variables are declared same they are in FM. Later on to save PO I am using FM BBP_PD_PO_SAVE.

Can anybody tell me what am I missing?

Thanks

Siddarth