Header and footer in whmcs client area

Hi,
I want to use only header and footer of my existing Wordpress website in WHMCS instead of WHMCS`s header and footer. I want to use default WHMCS template also.

How can I do it ?

I was try by creating a new page with [wcp_content] short code. Then I am getting error at # https://www.webhostingpeople.net/demo.html

Warning: Cannot modify header information - headers already sent by (output started at /home/webhosti/public_html/wp-content/plugins/wpmu-dev-seo/wds-files/wds-onpage/wds-onpage.php:64) in /home/webhosti/public_html/wp-includes/pluggable.php on line 896