As you’ve asked, I have disabled the plugin and tested again with a non-existing coupon.
The message “Vous souhaitez d’autres huiles ?” appears only once.
When I reactivate the plugin the message appears twice again.
So I don’t think it’s a theme issue or an issue with another plugin.
It only happens when WooCommerce Extended Coupon Features PRO is activated.
Any ideas what this could be ?
If there’s something else I can do to assist, please let me know.