I haven’t worked with Heroku, but I’ve copied my Gunicorn command below per chance it’s useful in some way:
/opt/rh/rh-python36/root/usr/bin/gunicorn --workers 5 --threads 2 --keep-alive 5 --preload --log-level info --capture-output --error-logfile /var/www/aar_customer/logs/aar_customer.log --pythonpath /var/www/aar_customer --bind 0.0.0.0:8051 aar_customer:server