Force redirect from HTTP to HTTPS via htaccess with multisite installation
move these lines

 RewriteEngine On
# Send would-be 404 requests to Craft
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/(favicon\.ico|apple-touch-icon.*\.png)$ [NC]
RewriteRule (.+) index.php?p=$1 [QSA,L]


to the end of the file