In case the chat widget does not appear and you have already whitelisted the url, it could be a problem with the apache settings itself.
In this case please open browser console on the site you have placed the chat widget. Should you see following error in the console:
Refused to display 'the url to your chat widget' in a frame because it set 'X-Frame-Options' to 'sameorigin'.
You will need to either change it in your apache config file or add following line on top of your htaccess file:
Header always unset X-Frame-Options