I want to set *an always* redirect from an old URL to a new URL. I have written this in the old server .htaccess file

RewriteEngine On

RewriteCond %{HTTP_HOST} ^oldserver\.com

RewriteRule ^(.*)$ https://sn.newserver.com/$1 [R,L]
Redirect /index.php https://sn.newserver.com/

But it doesn't work. Any idea?