How do I install multi-domain?

Hi there

I want to install the multi-domain plugin and I need single sign-on between these different sites as well. I am a bit confused about how to actually install the plugin.

From https://premium.wpmudev.org/project/multi-domains/ if I click on 'install', and then choose igsalesagency in the modal window, I get sent to
http://igsalesagency.co.uk/wp-admin/admin.php?page=wpmudev-plugins#pid=154

i get another modal here, and if I then click on 'download' it sends me back to the https://premium.wpmudev.org/project/multi-domains/ page.

So I am going round in circles. Nothing is downloading, and nothing new is appearing on the dashboard.

I am using Chrome on a mac.

Please can you advise what I am doing wrong.

kevin