The tail finish of my .htaccess reads:

RewriteCond %{query_string} ^(.*)$
RewriteRule ^([a-zA-Z0-9\-]+)/\?iframe x_iframe.php?pageurl=$1&%1 [L]

RewriteCond %{query_string} ^(.*)$
RewriteRule ^([a-zA-Z0-9\-]+)/?$ x.php?pageurl=$1&%1 [L]

What I am attempting to do is get it to ensure that any URL ending in '?iframe' utilizes a different page.

What shall we be held doing wrong?

Thanks.

You are able to only test the present URL path using the [cde] directive. The URL query are only able to be examined using the [cde] directive:

RewriteRule