tsearle left a comment (kamailio/kamailio#4250)
@xkaraman just to confirm, your build has the flag WITH_EVENT_LOCAL_REQUEST set?
as far as I can tell there should be no different between invoking via rpc and config script should end up at this call https://github.com/kamailio/kamailio/blob/4de3270830c08641e3bc3e585851324408...
and local_ack_rb will invoke the event callback if WITH_EVENT_LOCAL_REQUEST compile flag is set