Yes, you can use Really Simple SSL (Free) on multisite WordPress environments. It is important to note though that using Really Simple SSL Pro on multisite environments requires the dedicated Multisite version of the plugin, included with all of our Agency plans (25 sites and upwards).
Activating Really Simple SSL on a multisite environment has to be done in the Network Admin dashboard, via the Plugins page. Once ‘network activated’, the Really Simple SSL plugin will become active in all sites of the network.
After activating the plugin network wide, you will see a modal window where you are asked to activate SSL network wide. Note: activating SSL network wide will enable SSL for ALL sites of your multisite installation (even if a domain in the network does not have an SSL certificate).
