When installing drupal 8, or moving to production one could see this error. The fix is extremely simple.
This was a setting that was added to drupal 8 as a security measure. Long story short, this is an extra protection against http host header attacks.
Look for the $settings['trugsted_host_pattersn'] array in your settings file and uncomment if necessary. Next, add (all) your domains to the array. For example:
$settings['trusted_host_patterns'] = array( '^stefvanlooveren\.me$', '^.+\.stefvanlooveren\.me$', // also add subdomains like www.st... );
Save this, and your error will disappear. Moreover, your site is much more secure now!