ReadonlyactionOptional ReadonlyfieldsObject containing the Custom Fields fields for the shippingMethod.
Required if at least one Custom Field is defined as required in the `fieldDefinitions` of the referenced [Type](ctp:api:type:Type).
Optional ReadonlyshippingThe shippingKey of the Shipping to customize. Used to specify which Shipping Method to customize
on a Cart with Multiple ShippingMode.
Leave this empty to customize the one and only ShippingMethod on a Single ShippingMode Cart.
Optional ReadonlytypeDefines the Type that extends the specified ShippingMethod with Custom Fields. If absent, any existing Type and Custom Fields are removed from the ShippingMethod.
This action sets, overwrites, or removes any existing Custom Type and Custom Fields for the Cart's
shippingMethodorshipping.