Istraxx custom size plugin, products cannot be added to the shopping cart

[Leila]

Hi,
as the support doesnt answer my ticket posted a week ago, I'd like to ask my question here.

The products cannot added to the shopping cart after using the istraxx custom size plugin box. No "added to cart"  popup window shows up, the message in the shopping cart is "the product was successfully deleted from your shopping cart". Also the url of the cart is wrong, looks like https://www.kovrovik.com.ua/3515-4677-detail# instead of https://www.kovrovik.com.ua/cart
I use VM onepage checkout plugin but it works neither with the default VM cart nor with default template.

I.e. this page https://www.kovrovik.com.ua/3515-4677-detail

Joomla! 3.10.11
Virtuemart 4.0.12 10777
Onepage checkout plugin

Best regards
Liliia