ME_PROCESS_REQ_CUST Check Method

HI Experts

Am Using Check method in ME_PROCESS_REQ_CUST badi to validate item text , but i face problem that when i retrieve Purchase Requisition Number(BANFN) to read the text like this :

CALL METHOD

IM_HEADER->GET_DATA
receiving
    RE_DATA = ls_headerval .   " Header Data

BANFN come as rubbesh data like '#      1'

So i have tried with method post , it retrieved it fine , put i couldnt make validation in this method because transaction appear in display mode after excute method.

So please help me which method can i use it to validate PR before saving , an d it enable me to read PR number?

Regards

Ghadeer