If you support custom fields for Contacts we can use use them when creating or updating a contact. To do so we need an endpoint that returns the customers Custom Fields with their IDs.

GET /fields

{
  "custom_fields": [
		{
			"name": "Unsubscribed",
			"id": "7956yv02anehlhbey3o87yghfo"
		},
		{
			"name": "Responded",
			"id": "76qgerv7956yvey3o87yghfo09"
		},
		{
			"name": "Years at Current Position",
			"id": "87y56yv02anehlhghfoyv02a2e"
		}
	]
}

We do prefer that all fields including the default fields are included in the response