Saving product error

Hi,

If I look at the HTTP request and response from your server when I click on the save button, I can see this:
i.imgur.com/GEoiwqH.png
First you can see that the "status code" is "301, which indicates that something on the server is asking the browser to redirect somewhere else.
Then, you can see that in the "reponse", the location URL (where the browser has to redirect) is the same URL as the "request URL" (that is used by the button to send the "save" command to the server), but with the "el" language tag added to the URL.
This is an invalid URL and because of that, the website then redirect to the homepage as the URL is invalid.

So in short, your issue is that you have some translation/language redirection mechanism causing the issue even though such mechanism should only operate in the frontend of the website.
So the problem is not in HikaShop.
I checked your system plugins with the backend access you provided and if I disable the "System - Language Filter" plugin I do not have the error anymore.
I looked further into it and if I deactivate the option "Automatic Language Change" of the plugin while keeping the plugin activated, I also do not have the problem on your website.
If you look at the tooltip of that option, it says "This option will automatically change the content language used in the Frontend when a user site language is changed.". So there is no reason this plugin should mess with the URLs in the backend when that option is activated. To me, that's a bug of this plugin which needs to be reported to Joomla.
I checked the code of this plugin, but I'm not sure why it would do that, especially that it only happens for that product and not the others that I tested. I'm also not familiar with the code of this plugin so I'm not sure what to do. I suppose that the plugin is catching on something entered in the description or some other field of this product for some reason.