Hi,
I checked many pages and menus on your frontend, add a product to the cart, went to the checkout, etc.
Everything seems to be working fine.
So I don't see any issue and I don't know what your problem is.
Could you provide some screenshots ?
Are you able to reproduce the issue with another browser ? It might be something linked to caching on your browser maybe.
Or do you mean that you have an error in the backend of Joomla ? If so, what is the error page ?
Could you maybe provide some screenshots of the problem ?