Django Virtual Environment - No module named 'gunicorn'

I've followed this guide (https://www.digitalocean.com/community/tutorials/how-to-set-up-django-with-postgres-nginx-and-gunicorn-on-ubuntu-16-04), but I'm presently seeing the following when trying to run gunicorn via the gunicorn service file (/etc/systemd/system/gunicorn.service):

Oct 04 11:30:22 ukgcdeploy01 gunicorn[8095]:   File "/opt/envs/automation-console-env/bin/gunicorn", line 5, in <module>
Oct 04 11:30:22 ukgcdeploy01 gunicorn[8095]:     from gunicorn.app.wsgiapp import run
Oct 04 11:30:22 ukgcdeploy01 gunicorn[8095]: ModuleNotFoundError: No module named 'gunicorn'

The gunicorn.service file contains the following:

[Unit]
Description=gunicorn daemon
After=network.target

[Service]
User=root
Group=www-data
WorkingDirectory=/opt/envs/automation-console-env
ExecStart=/opt/envs/automation-console-env/bin/gunicorn --timeout 600 --log-level debug --error-log /var/log/automation-console-env_error.log  --access-logfile /var/log/automation-console-env_access.log --workers 3 --bind unix:/opt/envs/automation-console-env/automation-console-env.sock django_forms.wsgi:application


[Install]
WantedBy=multi-user.target

Running gunicorn manually works fine:

gunicorn --bind 0.0.0.0:8000 myproject.wsgi

This was previously working before I had to upgrade my Python version from 3.5.2 to 3.9, and due to some issues I ended up having to recreate the virtual environment, so I don't think it's necessarily an issue with the service file, but rather my Python/Gunicorn installation.

If anyone could offer some advice, it would be greatly appreciated :)

from Django Virtual Environment - No module named 'gunicorn'