If icons are displaying like strange characters or not showing up at all, this is most likely caused by a cross-origin error. You can fix it by adding the following code to the .htaccess file in the root directory of your website:

# Allow access from all domains for webfonts.
# Alternatively you could only whitelist your
# subdomains like "subdomain.example.com".
<IfModule mod_headers.c>
  <FilesMatch "\.(ttf|ttc|otf|eot|woff|font.css|css)$">
   Header set Access-Control-Allow-Origin "*"
  </FilesMatch>
</IfModule>

If this solution doesn’t work, please contact your hosting provider for assistance because the cross-origin error is server related.