ReadonlyactionOptional ReadonlyfieldsObject containing the Custom Fields fields for the BusinessUnit.
Required if at least one Custom Field is defined as required in the `fieldDefinitions` of the referenced [Type](ctp:api:type:Type).
Optional ReadonlytypeDefines the Type that extends the BusinessUnit with Custom Fields. If absent, any existing Type and Custom Fields are removed from the BusinessUnit.
Adding or updating a Custom Type on a Business Unit generates the BusinessUnitCustomTypeSet Message, removing one generates the BusinessUnitCustomTypeRemoved Message.