I have properly added sub-domain into DNS system.

DNS setting - https://ibb.co/e1L7KT

Apache configuration file:

<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName demo.mydomain.com
DocumentRoot /var/www/html/mydomain

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined

</VirtualHost>

I am not able to understand what is the issue exactly. I tried all the possible ways to fix this issue but unfortunately could not solve it.

Any help will be appreciated.
Thanks