ReadonlyactionOptional ReadonlyexternalAn external Tax Rate can be set if the Cart has the External TaxMode.
Optional ReadonlyshippingValue to set. If empty, any existing value will be removed. If the referenced Shipping Method has a predicate that does not match the Cart, an InvalidOperation error is returned.
To set the Cart's Shipping Method, the Cart must have the
SingleShippingMode and ashippingAddress.