Hi,
Create an implementation of badi BBP_DOC_CHECK_BADI for SC (put in the filter BUS2121)
Call the FM BBP_PD_SC_GETDETAIL to get the PARTNERS table, check if there is an entry for PARTNER_FCT = 00000019 and DEL_IND = space for all the items.
If not populate the export table ET_MESSAGES with your message.
Regards,
Ricardo.