Display not appearing at all in CMS

I have installed a CMS on one Ubuntu 16.04 machine, and a client on a Ubuntu 12.04 machine. Both machines are connected via ethernet to the same switch, so they can find each other. I can navigate to the CMS from the browser of the client machine.

However, despite giving the client machine the URL and the server key of the CMS, the CMS does not see any displays. What am I doing wrong?

Here is the site.cfg.default file for the client:

Here is the configuration of the CMS:

Here is what I see under the Displays tab:

Python client is no longer developed/supported.
It probably doesn’t work because you’ve 1.7.7 CMS, you’d need 1.6.4 CMS version to work better with python client.

Installation manual just in case: http://xibo.org.uk/manual/en/install_python_client.html

Okay, so what do I do? Use Windows 7 for the client machines instead?

There are currently two working clients - Windows and Android.

So, yes if you do have a Windows machine then use Xibo for Windows.