i found the bug with wpml(translation). your portail don’t work if i check the option “Translate Everything”
i look your pricture. this working on this screen but if you click on “view cart” the ajax don’t put the product on cart. on the next screen you have cart empty
In WPML there is a setting “Languages – set Store language cookie to support filtering for AJAX” which you need to turn on or enable then it will work.