Hi,
Thanks for the accesses.
We made a patch on your website, patch which would be include in the next release of HikaShop.
In the class cart, we replaced
			$old_coupon = $app->getUserState( HIKASHOP_COMPONENT.'.coupon_code','');
			if($old_coupon == $new_coupon){
				return false;
			}By
			$old_coupon = $app->getUserState( HIKASHOP_COMPONENT.'.coupon_code','');
			if(!empty($old_coupon) && $old_coupon == $new_coupon){
				return false;
			}In order to be sure to remove the coupon evenif there is a problem with the session.
Regards,