Sending Custom fields from SRM to ECC through BAPI

Dear All ,

I am looking for a step by step instructions on how to send my data i.e Start date and end date at ITEM :LEVEL for limit items from SRM to ECC

It is currently only sent a Header level . I have almost read all the posts and yet not able to figure out . Please can you some one help me to understand .

Checked the below

How to use BAPI extensions?

Using BAPI_PO_CREATE to create a PO with reference to another PO/item

Fill ZZ item fields BAPI_PO_CREATE1 - EXTENSIONIN

BAPI_PO_CREATE1 and EXTENSIONIN structure

and also  checked the SAP official page :

http://wiki.scn.sap.com/wiki/display/ABAP/BAPI?original_fqdn=wiki.sdn.sap.com#BAPI-Passingcustomfields

Transfer process of the Shopping Cart

How to transfer custom fields from SRM to Backend

However no luck . I also opened a similar thread previously but still unable to get an end to end understanding .Please could some one guide me for this one ?  Currently what I found out there is a class CL_BBP_BS_ADAPTER_PO_CRT_ERP10 where CREATE_DOCUMENT decides what fields would be passed .. In that there is a FM which is being called from ECC .. and in that there is header and header X field ..

which has the fields which I need VPER start and end date ..

CALL FUNCTION 'BAPI_PO_CREATE1'
       DESTINATION av_rfc_dest
       EXPORTING
         poheader               = as_po_out-is_poheader      "#EC ENHOK
         poheaderx              = as_po_out-is_poheaderx

Now I wnat the same fields to be passed at item level of the SC .. Please could you confirm on what exactly I should do ?

I saw the below tables not sure what I should do with them to include the 2 fields I want which should be passed to ECC .

TABLES

          poitem                 = as_po_out-it_poitem        "#EC ENHOK
         poitemx                = as_po_out-it_poitemx       "#EC ENHOK
             extensionin            = as_po_out-it_extensionin   "#EC ENHOK
  *      extensionout      = as_po_out-it_extensionout "not used by SRM
          poexpimpitem      = as_po_out-it_poexpimpitem      "#EC ENHOK
          poexpimpitemx     = as_po_out-it_poexpimpitemx     "#EC ENHOK
         potextheader      = as_po_out-it_potextheader "not used by SRM
*      popartner         = as_po_out-it_popartner    "not used by SRM

Please can some one let me know for the below queries :

1, How to identify If I am checking on the right method .

2. How I can create these 2 fields voer start date and end date and pass them to EKPO table of PO in ECC ?

3. How to create these 2 fields in BAP and pass it further from SRM to ecc

4. How would they be visisble in SC portal screen ..

Please guide me on this would be really grateful . Thanks in advance for the help

Regards

Vinita