I\'m trying to use the [L] flag in RewriteRule, but it doesn\'t seem to work. I\'d like that if you call the page:
www.domain.com/admin
Your second rule is strange. I do not know what you are attempting to do by putting $1 as the value you are checking your condition against. It should probably look like this:
RewriteEngine on
RewriteRule ^admin/(.*) /backend.php/$1 [L]
RewriteCond %{REQUEST_FILENAME} !^(index\.php|admin|assets|images|uploads|robots\.txt|backend\.php)
RewriteRule ^(.*)$ /index.php/$1 [L]
Note I have also added a pass-through for backend.php