Apache Server is not reachable

Based on your description it sounds like you're using localhost as the server name. That's always the local computer as pointed out in the comments. You would need to 1) configure Apache to listen on a name other than localhost (it appears you were trying to use webdev), 2) add a record to your DNS server on your local network called webdev to point at the IP of mytestserver, or alternatively add a record to the HOST file pointing to the IP of that server on the test client machine (not 127.0.0.1), and 3) make sure your firewall is open to accept connections on port 80. You could also simply request the site via the network IP of the mytestserver machine (also not 127.0.0.1, check ifconfig) if that's the default site for your apache configuration.

The problem was the apache conf. Port 80 was open ... but listening on :::80
I changed the "Listen" address in the config from this:

Listen 80

to this:

Listen 0.0.0.0:80

And now it works. I can launch the site from the remote machine.