My client requirment is .
Currenty system checks the BUKRS,LIFNR,WAERS,XBLNR,WRBTR,BLDAT for duplicate invoice this is a standard SAP functionality for T.code MIR7.
Logic needs to be changed
Duplicate Check in SAP for Vendor invoices to only check Vendor number (LIFNR) and Reference number (XBLNR).
I have found a function module which is used to through the error message CUSTOM_MESSAGE is the FM under MRM_FI_DOCUMENT_CHECK. advise what can be done for this.