How to stop the posting duplicate invoice from IDOC?

Hi Experts,

                    We have a requirement to stop the duplicate the invoice's and if any duplicate inovoice is posting wihout closeing already existing inovice raise the error message in IDOC status.

I have searched the SCN before posting thread and tried with implemented the EXIT_SAPLMRMH_015 exit , but is not useful.

IDOC is trigering through IDOC_INPUT_INVOIC_MRM  fm as inbound.

Please help me on the same.

Thanks,

in Adv.