Environment variable in config

I am getting errors addressing environment variables. Are they supposed to work in such sections. Not really clear from this[1] page.

service health-check { # example health-check. executable = script -p /bin/health-check.sh inet_listener health-check { port = env:PORT0 } }

[1] https://doc.dovecot.org/configuration_manual/config_file/config_variables/