Characteristics not retained in checkout

Hello,

That kind of problem is mostly due to an override of your product page.
If there is some HTML errors in the page (break the DOM) ; instead of submitting only the selected variant, it will submit all variants data.
In such case, we first recommend to (backup) remove the view overrides ; or you can change temporally your template to the default Joomla one (so a template without overrides).
If the idea was the good one then it will need to fix the HTML errors in the view override so the "<form>" in the product page won't be broken anymore.

Regards,

Hi,

Customizing the product page is not a problem. The problem is that you've made some mistakes in the HTML.
If you check the HTML of the page with the browser's inspector, you can see that the hidden data of the variants of the product are inside the form tag of the page:
monosnap.com/file/U0DlkVTRyK1iYDHjFyd9JWP9VJYant
Normally, that data is outside the form. Because of that, when you click on the "add to cart" button, it submits the data of the selected variant, and then the data of each variant. This leads to the server only seeing the data of the last variant. And thus, regardless of what you select it's always that variant that gets added.
This indicates that you're missing some closing div tags near the end of the view files that you've customized or something like that.
If you check the HTML with the default template of Joomla, you'll see that the hidden data of the variants is outside of the form tag by default, so you just need to make sure that it's still the case with your customization.