Tested with BSD NetCat, not nmap project's NCat!
CLIENT
IP=
CHANGEME ; for ((i=1; i<=600;i++)); do echo "$i: Received at $(date '+%s')." | netcat -4unNw1 ${IP} 15384; done
SERVER
Ubuntu 20.04.3
echo "$(dig +short myip.opendns.com @resolver1.opendns.com)"; netcat -vulknp 15384