I am trying to rewrite a specific PHP file GET parameter but cant seem to get things to work.
I want to rewrite http://www.example.com/meeting.php?ref=y0fpjXrrGP
You don't need to add that to .htaccess, if your URL is inside your Wordpress, you need to add them to the rewrite URL
Check this: How to create custom URL routes?
Hope it helps.
Just use this in your .htaccess
file:
RewriteEngine On
RewriteRule ^meeting/([^/]*)$ /meeting.php?ref=$1 [L]
It will leave you with the URL: http://www.example.com/meeting/y0fpjXrrGP
Make sure you clear your cache when testing this.