Thanks, it was a dumb error.
Ok now the script *seems* to send the data (at least it doesnt reload the page)
But after clicking the submit button, the basket is still empty
When sending the form, a product is supposed to be added to the basket here:
https://nidieunimaitre.spreadshirt.com/shop/basket/
It works when i use a normal form, but doesn't work when i try to submit with AJAX