Add the following line to your wp-config.php file. It can be placed anywhere above the /* That’s all, stop editing! Happy blogging. */ line.
/* Multisite */ define( 'WP_ALLOW_MULTISITE', true );
Go to https://<your domain>/<site name>/wp-admin/plugins.php
Select “Deactivate” as the bulk action. Click in the box above the list of plugins to select all of them and click on the Apply button.
In the bar at the left of the page go to Tools/Network Setup”. It will give you some more code to add to your wp-config.php file. There is no need to follow the advice to backup.
Replace the entire contents of the .htaccess file with the text below followed by the code they say to to go into the .htaccess file.
# HTTPS
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]
# END HTTPS
Then login again at https://<your domain>/<site name>/wp-login.php and go to MySites/Network Admin/Plugins (top left of the page and Network Activate all plugins.
Please note that when logging in as super-admin for multisite there is the control of the whole network with its own Dashboard, Sites, Users, Themes, Plugins and Settings as well as control of individual sites. This is accessed from the top left hand corner of the screen with an icon with three little houses and the text “My Sites” which is a pull down menu with Network Admin and then all the individual sites within the multisite network.
There will be a couple of messages from the SG Optimizer – tell it to ignore having the wrong version of php.
Go to MySites/Network Admin/Dashboard. Then go to “Settings/Disable Comments” and select Everywhere as this is not a blog.