Old thread, but posting for anyone else who needs this information.
Edit pushover.sh in /boot/config/plugins/dynamix/notifications/agents/ to include -F "device=my device" \. Change my device to whatever your device name is within the Pushover dashboard.
#!/bin/bash
############
USER_KEY="user key"
APP_TOKEN="app token"
MESSAGE="$EVENT\n$SUBJECT\n$DESCRIPTION"
############
MESSAGE=$(echo -e "$MESSAGE")
case "$IMPORTANCE" in
'normal' )
PRIORITY="-1"
;;
'warning' )
PRIORITY="0"
;;
'alert' )
PRIORITY="1"
;;
esac
curl -s -k \
-F "token=$APP_TOKEN" \
-F "user=$USER_KEY" \
-F "device=my device" \
-F "message=$MESSAGE" \
-F "timestamp=$TIMESTAMP" \
-F "priority=$PRIORITY" \
-F "html=1" \
https://api.pushover.net/1/messages.json 2>&1