How to convert multisite subdomain from http to https

I like a simple, all-purpose htaccess to enable https on all site requests:

RewriteEngine On

RewriteCond %{HTTPS} !=on

RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301] 

In addition, go into Network Admin, Sites, then Edit each site, then the Settings tab for each site. Change all occurences of http to https for your site. (Some plugins may have the http, so changing them will get rid of the ‘mixed’ warning in browsers.)

Plus, you will need to change all media URLs on all sites. That’s easiest with a search/replace plugin (I like “Better Search and Replace”, but check the plugin you choose that it supports multisite) to change http://www.example.com to https://www.example.com (using your domain name).

Although the above htaccess might take care of http in plugins/themes/media/etc, I like a more complete process, so I change everything as needed. Backup your database first, of course.