Subdomain setup for Flask + apache

Question

I have installed and deployed Flask on a CentOS server but the subdomain for some reason, is not working properly. I really need some help on this one. I am actually a newbie in this field so please be a little gentle.

Here are the details:

1. CentOS 7
2. Python 3.6.4
3. Apache/2.4.6 (CentOS)

My flask application is structured like this:

/home/user/web/mysite.net/
  wsgi.py
  runserver.py
  mysite/
    __init__.py
    views.py
    ...

And inside views.py I have this snippet below to setup the subdomain "sub".

@app.route(rule='/', subdomain='', strict_slashes=False)
def index():
    return "Index page"

@app.route(rule='/', subdomain='sub', strict_slashes=False)
def sub():
    return "Subdomain working"

My conf files are setup like this:

I have a conf file called main.conf which basically just points to the other conf files namely:

 - mysite.net.httpd.conf
 - mysite.net.httpd.ssl.conf
 - sub.mysite.net.httpd.conf
 - sub.mysite.net.httpd.ssl.conf

This is what's inside mysite.net.httpd.ssl.conf:

<VirtualHost xx.xxx.xxx.xxx:443>
    ServerName mysite.net
    ServerAlias www.mysite.net
    ServerAdmin admin@mysite.net
    WsgiDaemonProcess mysite user=apache group=apache threads=2
    WSGIScriptAlias / /home/user/web/mysite.net/wsgi.py
    <Directory /home/user/web/mysite.net/mysite/>
        Order allow,deny
        Allow from all
    </Directory>

    SSLEngine on
    SSLVerifyClient none
    ...

</VirtualHost>

,for sub.mysite.net.httpd.ssl.conf:

<VirtualHost xx.xxx.xxx.xxx:443>
    ServerName sub.mysite.net
    ServerAdmin admin@mysite.net
    WsgiDaemonProcess sub.mysite user=apache group=apache threads=2
    WSGIScriptAlias / /home/user/web/mysite.net/mysite/wsgi.py
    <Directory /home/user/web/mysite.net/mysite/mysite/>
        Order allow,deny
        Allow from all
    </Directory>

    SSLEngine on
    SSLVerifyClient none
    ...

    ErrorLog /var/log/httpd/sub_error_log
</VirtualHost>

I have also added this in the dns settings:

sub   A  xx.xxx.xxx.xxx

The index page is working fine but when I try to access sub.mysite.net it just shows the same as the index page. Any h