Default URL: domain.com/contact.php
Rewrite URL to: domain.com/contactus
Then when I have to enter the default URL to: domain.com/contact.php it should redirect (open) to domain.com/contactus
I have tried
RewriteRule ^contactus$ contact.php [L]
RewriteRule contact.php contactus [NC,R=301,L]
You need one redirect rule to force new URI in browsers and one rewrite to forward new URI to php file:
RewriteEngine On
# redirect rule
RewriteCond %{THE_REQUEST} \s/contact\.php[?\s] [NC]
RewriteRule ^ /contactus? [L,R=301]
# rewrite rule
RewriteRule ^contactus/?$ contact.php [L,NC]
? in target URI will remove existing query string.