The Free Freight promo has been updated so that checkout is prevented if the promo carrier is not valid for the products on the order.

The user will now be shown a message ("There are products on the order that cannot be sent by {carrier name} - please remove promo code") if the products on their order can't be shipped by the free freight carrier. This might happen if the product(s) are oversize or exceed the carrier's weight limit, for example.