Website doesn't work under Linux, but works under Windows/Mac

I'm trying to buy a product on https://qinao.de/ with my (Arch) Linux laptop and different Browsers (Chrome, Firefox). But I can't add products to the Cart (and some images don't load). It works fine on my mobile phone, and on my friends' laptops with Windows and Mac. I've never seen anything like this. Can anybody with Linux confirm this, and perhaps can decode the error messages on the Developer console? Shouldn't the functioning of a website depend entirely on the browser and not the operating system? Thank you!