TERMID error in MESG command to Operator

Q:

Message to Operator give RC=255 with these messages:
     MESG OPER                          SENT=> DBDCICS
     TERMINAL ID ERROR IN "MESG " COMMAND - TERMID = OPER
     COMMAND FAILURE - RETURN CODE HAS BEEN SET

A:

The OPER operand is only available if you have our CICS/Message product installed. Without CICS/Message,  you may only send messages to given termid.