Why don’t you use the System reply List (WRKRPYL). Specify BRM1033 with a reply value set to ‘C’. Don’t forget to modify your JOBD parameter INQMSGRPY to *SYSRPYL.
I’m not aware of <b>any</b> message that can be monitored for and that will also accept a reply. You monitor for *ESCAPE, *STATUS or *NOTIFY messages. But you would reply only to *INQ (inquiry) messages.
Further, you monitor for messages that appear on the program’s message queue. But your SNDRPY command is trying to send a reply to the QSYSOPR user message queue.
A MONMSG wouldn’t be appropriate. The condition has been signaled and the STRBKUBRM command has ended at the time your MONMSG receives control.
The system reply list is possibly a good alrenative for what you’ve shown. If you could explain your actual business problem, a more precise and appropriate solution is probably available.