Update custom field through BAPI_INCOMINGINVOICE_SAVE

Hi,

Need to update custom field through BAPI_INCOMINGINVOICE_SAVE on RBKP table(custom field zabcd).

I have added custom field(zabcd) to IVEXT table.

Filled extension table IVEXT as a Structure and Field value) to Valuepart1 and passed to bapi extension structure(EXTENSIONIN)

But custom field is not updating with value in incoming invoice(rbkp-zabcd custom field),

in debugging i found below badi's but those are SAP Internal use.

MRM_BAPI_MAPPING,

MRM_IVEXT_PROCESS.

Please suggest me is there any user exits or any Badis to implement the logic to update custom field in incoming invoice through BAPI BAPI_INCOMINGINVOICE_SAVE.

Thanks

Indra