I am trying to start Gunicorn from systemd service file, but I get import module error. How can I fix it?

My gunicorn service file:

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

[Service]
User=sammy
Group=www-data
WorkingDirectory=/home/sammy/myproject
ExecStart=/home/sammy/myproject/venv/bin/gunicorn --workers 3 --bind unix:/home/sammy/myproject/myproject.sock myproject.wsgi:application

[Install]
WantedBy=multi-user.target

When I execute gunicorn --bind 0.0.0.0:8000 myproject.wsgi:application, there is no error.

But when I use

sudo systemctl start gunicorn
sudo systemctl enable gunicorn

I get this error:

ImportError: No module named 'myproject'

What is wrong?