ReadonlyactionOptional ReadonlyexternalAn external Tax Rate can be set if the Cart has the External TaxMode.
Optional ReadonlyshippingValue to set. If empty, any existing value is removed.
If the referenced Shipping Method is inactive, or has a predicate that does not match the Cart, an [InvalidOperation](ctp:api:type:InvalidOperationError) error is returned.
To set the Cart's Shipping Method the Cart must have the
SingleShippingMode and ashippingAddress.