Client cant see the Updated dynamic content

Yeah that’s definitely a caching issue. The code you have there should handle it but you can’t really guarantee anything.

Do you have a caching plugin installed? If so try disabling that.

Also in your wp-config.php file see if you have this define('WP_CACHE', true); if so change it to false. If it isn’t there add it but make that false.

That’s really all, in my experience, you can do from our end unfortunately.