BAPI_PO_CREATE1 with Invoice plan

Hi Guys,

I am trying to create Service Task Order with invoice plan, reference to contract using BAPI_PO_CREATE1, i am able to create STO but the invoice plan details are not getting passed to STO.

Below is part of my code. Can any one suggest me why invoice plan details are not coming in STO.

**Invoice

*Date

invoiceplanheader-doc_item = '00001'.

invoiceplanheaderx-doc_item = '00001'.

*CATEGORY

invoiceplanheader-category = '2'.

invoiceplanheaderx-category = 'X'.

*Inv type

invoiceplanheader-ip_type = '20'.

invoiceplanheaderx-ip_type = 'X'.

*Inv date

invoiceplanheader-start_date = sy-datum.

invoiceplanheaderx-start_date = 'X'.

*Billing plan

invoiceplanheader-period = '01'.

invoiceplanheaderx-period = 'X'.

*Sort field

READ TABLE it_field INTO wa_field INDEX 3.

invoiceplanheader-sort_fld = wa_field-value.

invoiceplanheaderx-sort_fld = 'X'.

*Inv Item

*Item

invoiceplanitem-doc_item = '00001'.

invoiceplanitemx-doc_item = '00001'.

*Inv value

invoiceplanitem-bill_value = wa_po_amt.

invoiceplanitemx-bill_value = 'X'.

*Date desp

invoiceplanitem-date_desc = '0001'.

invoiceplanitemx-date_desc = 'X'.

APPEND : invoiceplanitemx, invoiceplanitem,

invoiceplanheader, invoiceplanheaderx.

ENDAT.

ENDLOOP.

CALL FUNCTION 'BAPI_PO_CREATE1'

EXPORTING

poheaderx = poheaderx

poheader = poheader

IMPORTING

expheader = expheader

exppurchaseorder = exppurchaseorder

TABLES

poservices = poservices

posrvaccessvalues = posrvaccessvalues

return = return

poitem = poitem

poitemx = poitemx

poaccount = poaccount

poaccountx = poaccountx

invplanheader = invoiceplanheader

invplanheaderx = invoiceplanheaderx

invplanitem = invoiceplanitem

invplanitemx = invoiceplanitemx

EXCEPTIONS

OTHERS = 01.

.