GR based BAPI_INCOMINGINVOICE_CREATE payment terms issues!!

hello friends,

I am using BAPI_INCOMINGINVOICE_CREATE for posting of

GR based Invoice verification (Alternation to MIRO).I am able to post the document through

BAPI if and only if ::-

1) i specify payment terms(PMNTTRMS in header data of BAPI) in coding

or

2) if my purchase order contains payment terms .

I have some issues using this BAPI::

1) i want to post BAPI for purchase orders and vendors which doesn't have

any payment terms , in this case BAPI gives and error message "specify correct payment terms"

Current SAP version is SAP4.7 enterprise with SAP_APPL at 23 number

Looking forward for response

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