How to link WHMCS WP Plugin links to Wordpress Menu

I am attempting to directly link a WHMCS page to the WP Menu, but it will not work. Wordpress strips out the bracks [page]. For example, I am trying to insert the URL:

http://domain.com/?whmcsportal%5Bpage%5D=whmcs%3A%2F%2Fdomain.com%2Fwhmcs%2Fclientarea.php

But upon save, it changes the URL to:

http://domain.com/?whmcsportalpage=whmcs%3A%2F%2Fdomain.com%2Fwhmcs%2Fclientarea.php

You'll notice the brackets were removed.