Responsive option doesn't work

Hello dear developer!
I installed your great Slideshow CK module, but responsive option doesn't work on my website gorizont-optika.ru/ .
I have image.jpg (full width) in /media/com_slideshowck/images/slides
As well as image.jpg (640px) in /media/com_slideshowck/images/slides/640
Button "Use specific images for Mobile" is enabled.
But on mobiles the full width image is still displayed.
Would you be so kind to help me with this issue please?

Hi
in fact it works. If you load the page and reduce your browser it has no effect, because it won't load a 2nd image in the same page, it would be bad
you must load the page with a screen <= 640px wide, then the script will take the small image instead of the normal one, to save some bandwidth (assuming that you are on mobile)
you can also replace the "640" images with your own, if you want to load different images on mobiles
CEd

Thanks for your reply.
However, how can I make sure that this works? Because when I check it in browser for mobile devices it doesn't work.
Screenshot attached.

you can use the console of your browser to check the source code and see the images that are called.
Tested by my side with a browser at less than 640px, loaded the page, the images are loaded in the "640" folder

Unfortunately not. As you can see from the screenshot bellow, for device 375px width images are loaded from folder /images/slides, not from folder /images/slides/640

this is not the correct place to check
Please look at this screenshot