Raspberry Pi OS - at command does nothing - linux

Question

I have a Pi 3B+ with Pi OS (PRETTY_NAME="Raspbian GNU/Linux 10 (buster)")
I want to run a script at a certain time, using at command.
For testing purposes i have made a test1.sh, to open Chromium browser using pyautogui.
This file is located in /home/pi/test1.sh and contains the following:
#!/usr/bin/python3
import pyautogui
pyautogui.click(67, 20) #click Chromium icon
This .sh executes fine when clicked in the GUI and also when I run it typing ./test1.sh in the Terminal.
Trying to use at command does not work and yields the following:
pi#raspberrypi:~ $ at 11:50
warning: commands will be executed using /bin/sh
at> ./test1.sh
at> < EOT> (Here is where I type ctrl+D)
job 11 at Fri Nov 5 11:50:00 2021
At the specified time, nothing happens. I know it must be something I am doing wrong, but for the life of me I can not figure out what it is. Help?
Edit:
the first / in the shebang was missing in the post, but not in the file.
atq returns nothing
ps ax returns text below (cut for brevity)
PID TTY STAT TIME COMMAND
1 ? Ss 0:05 /sbin/init splash
2 ? S 0:00 [kthreadd]
3 ? I< 0:00 [rcu_gp]
date returns accurate date and time
cat /var/mail/pi returns the following:
Subject: Output from your job 11
To: pi#raspberrypi
Message-Id: <E1miwnI-0000tR-83#raspberrypi>
From: pi#raspberrypi
Date: Fri, 05 Nov 2021 11:50:00 +0100
sh: 49: ./test1.sh: not found
From pi#raspberrypi Fri Nov 05 12:05:00 2021
Return-path: <pi#raspberrypi>
Envelope-to: pi#raspberrypi
Delivery-date: Fri, 05 Nov 2021 12:05:00 +0100
Received: from pi by raspberrypi with local (Exim 4.92)
(envelope-from <pi#raspberrypi>)
id 1mix1o-0000xA-KG
for pi#raspberrypi; Fri, 05 Nov 2021 12:05:00 +0100
This suggests that the file is not there, but when I type ls it is clearly shown.
Using the full path /home/pi/test1.sh also returns nothing but the mail received states the following:
Subject: Output from your job 13
To: pi#raspberrypi
Message-Id: <E1mjHmv-0000NT-4B#raspberrypi>
From: pi#raspberrypi
Date: Sat, 06 Nov 2021 10:15:01 +0100
Traceback (most recent call last):
File "/home/pi/test1.sh", line 3, in <module>
import pyautogui
File "/home/pi/.local/lib/python3.7/site-packages/pyautogui/__init__.py", line 249, in <module>
import mouseinfo
File "/home/pi/.local/lib/python3.7/site-packages/mouseinfo/__init__.py", line 223, in <module>
_display = Display(os.environ['DISPLAY'])
File "/usr/lib/python3.7/os.py", line 678, in __getitem__
raise KeyError(key) from None
KeyError: 'DISPLAY'

Answer 1

As pointed out by #linuxfan in the comments:
The DISPLAY variable is not set.
problem was fixed by doing the following:
pi#raspberrypi:~ $ at now + 1 minute
warning: commands will be executed using /bin/sh
at> export DISPLAY=:0.0
at> /home/pi/test1.sh
at> <EOT>
job 17 at Sun Nov 7 10:55:00 2021