ReadonlyactionOptional ReadonlyexternalValue to set. If empty, any existing value is removed.
Optional Readonlyshippingkey of the ShippingMethod to update.
This is required and valid only for Carts with Multiple ShippingMode.
An InvalidOperation error is returned if shippingKey is provided for Carts with Single ShippingMode, or omitted for Carts with Multiple ShippingMode.
A Shipping Method tax amount can be set if the Cart has the
ExternalAmountTaxMode.