To create a project, use this endpoint.
To add a custom field to a project, you pass in the custom field object to this endpoint. The custom field must already be created, you can do that by using V3 Custom Fields. Once the custom field is created, it’s available to attach a project. See sample payload below.
To update or delete custom fields from a project pass an empty array for the customFields param. Example on Updating a project.
To test that the custom field was added, you need to use the V2 projects endpoint with “includeCustomFields=true” to return the custom fields and their values.