Update customer custom fields

Custom field value. For purchase order entries (isPurchaseOrder: true), this is the new PO number. Pass an empty string to unset the PO. Max 48 characters apply to PO values.

Manufacturer custom field ID. Required when isPurchaseOrder is not true.

Set to true to update the customer’s active purchase order instead of a manufacturer-defined custom field. When true, manufacturerCustomFieldId is ignored and customFieldValue is used as the PO number.