this is what works for me:
go to:
/wp-content/plugins/plugin name/plugin-fw/license/lib/yit-plugin-license.php
delete the entire following code:
if ( !!$product_names ) {
$start = '<span style="display:inline-block; padding:3px 10px; margin: 0 10px 10px 0; background: #f1f1f1; border-radius: 4px;">';
$end = '</span>';
$product_list = '' . $start . implode( $end . $start, $product_names ) . $end . '';
$activation_url = self::get_license_activation_url();
?>
Warning! You didn't set license key for the following products:
which means you're missing out on updates and support. '>Enter your license key, please.
<?php
}
by doing this, the nag message will stop completely. but you have to do that in every YITH plugin you have installed.
goodluck