There is a bug in OpenCart 188.8.131.52 where additional emails are not being saved properly. This is an ocmod fix for that issue.
To install this in your opencart 184.108.40.206, download and extract the content, you will find a zip file with .ocmod.zip extension. Go to Admin : Extension > Extension Installer , and upload this zip file. Then Go to modifications and refresh. Now you should be able to add additional emails in your setting.