I already install nignx hepler in my website. But the purge cache cant work

I already install Nginx hepler in my website. But the purge cache cant work. I need to clear the cache manually.

I establish the Nginx cache folder in
run/Nginx-cache
and add
define('RT_WP_NGINX_HELPER_CACHE_PATH', '/run/nginx-cache'); in wp-config file.

Anyone can help me?