i did follow these steps and added the line to the index.php
HikaShop uses the core Joomla messaging system to display messages on your website so if you don't see any message when you don't enter correct information during the checkout process, that's probably because your Joomla template does not contain the tag to display Joomla messages: <jdoc:include type="message" />
Or sometimes, your template has an option to turn that display off. So first, check about such option in your template options screen and turn it on.
If you don't find it, please edit the index.php file from your template and make sure the tag <jdoc:include type="message" /> is added to it.
If not, please add it just before the tag <jdoc:include type="component" />
This tag should already be present in all templates.
but still blank popups...