unable to access domain website

Dear experts,
I've used site to site VPN connection to connection two different LAN together. one is under 192.168.100.xxx and the other is under 192.168.101.xxx

When I tried to test out the web server on a WAMP stack, I was able to access with the PC from 192.168.100.xxx but having problem with the 192.168.101.xxx

I've created a host name for the web server which is 192.168.100.66 which is web.app

If I tried to access from the same subnet, I am able to run the web page without any issue.

If I tried to access from the different subnet, I need to type in the IP as in 192.168.100.66 instead of web.app

Here is example:

http://190.168.100.66/system/list.php <-- I have to type this if I want to access from different subnet.
http://web.app/system/list.php <-- I can access this or the above if I am in the same subnet as my web server.

I wish to know how can I resolve this and allow users from different subnet to simply access my web by typing http://web.app/ instead of http://192.168.10.66? Is there a way that I can reconfigure this either in apache.conf or httpd.conf, or php.ini? Thanks.