notify-send not working from script - but works from CLI

Question

Good Day, I am new to Linux (Raspberry) and am trying to get notify-send to work from a script (see below).

Notify send works from the terminal CLI and displays on my GUI. But it does not work from the script. I am using Raspberry Buster - with all updates.

#!/bin/bash

# This should point to the pivoyager executable
PIVOYAGER=/usr/local/bin/pivoyager

while true;
do
   # Phase 1: Check every 5 seconds if we are USB powered.
   #          If we are not on USB power, go to phase 2.
   while $PIVOYAGER status flags | grep "pg";
   do
      sleep 5
   done


   # Phase 2: Do something before shutdown. (optional)
   #          e.g. send an email, warn users, etc.
   #notify-send "We are on Battery Power.  Save all your work."
   sleep 30



   # Just check if power was miraculously restored.
   if ! $PIVOYAGER status flags | grep "pg"; then
      break
   else
      notify-send "Power was restored. Shutdown aborted!"
   fi
done

# Phase 3: Initiate the shutdown.
#          - Enable automatic power on once USB power is restored.
#          - Program full power cut in 25 seconds.
$PIVOYAGER enable power-wakeup
$PIVOYAGER watchdog 25
sudo shutdown now

Thanks in advance for your help.