Modif : Actually I forgot that I have a custom plugin doing some custom redirect "onBeforeCartSave". It is probably not compatible with this version.
I need to go further
Don't consider below
Several years I practice Hika. Sure it should be "obvious" but can't find it...
The site is a dev one to check our ability to bring our prod site from J3/PHP 7.3/ Hika 4.2.2 to a pre-J4 version (php8 uptodate)
So the dev is an upgraded clone of our prod site (which may have "bring" some custom hack/override I may have forgotten).
Here is the page display product :
This message contains confidential information
Our purpose is to send the customer to the checkout directly as soon as he clicks on "add to cart".
Most of our products need to be logged in for that.
It works well "out of the box" when you are connected (if I disable the cart notification plugin)
But if the user is not connected (guest), instead of redirecting to the login page is throws a "cart_id was not returned in addToCart AJAX call" message in the browser console.