Solution 1. Regardless of what type of website you have, your site needs an SSL certificate. How to get a Free SSL Certificate for your WordPress website: https://nycreatis.com/wp/FreeSSL
Solution 2. The site has disabled wp-cron. Check the wp-config.php file. Delete this line: define(‘DISABLE_WP_CRON’, true);
Solution 3. Make sure the latest version of the plugin is installed. Reinstall the plugin.