If you need to redirect all the traffic from a subdirectory to the root of the site, use the htaccess below.
For example: www.domain.com/hello/ -> www.domain.com
The htaccess below will use the relative URL redirect to go to the root of the site.
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# Redirect /subdirectory/ to root url
# see: https://www.jucra.com/whmcs/knowledgebase/181/
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RewriteRule ^SUBDIRNAME/(.*)$ / [R=301,NC,L]