We’ve added a new settings screen for managing custom client fields (requires admin role). Custom fields allow you to customize the client object for tracking unique attributes or data. In addition to viewing and editing these fields on individual client records, they can be edited inline on the Clients screen, used for custom segments, and accessed via the API.
Custom fields can also be added to the contact object.
This article contains additional details about custom fields, including the available data types and default values.