🚧
Organization-Related Nodes Have Been Deprecated
Contact-Organization relationships are now managed through Account-Contact end points

📘
Reference a custom field by id- not the custom field's name/title.
When writing to a Contact's custom data, the field must be the id of a previously-created custom field, not the custom field's name/title.

Creating a custom field

Creating a custom field value

Retrieving previously-created custom fields

{
  "contact": {
     "email": "johndoe@example.com",
     "allowNullEmail": true,
     "firstName": "John",
     "lastName": "Doe",
     "phone": "7223224241",
     "fieldValues": [
               {
                    "field": "1",
                    "value": "The Value for First Field"
               },
               {
                    "field": "6",
                    "value": "2008-01-20"
               }
          ]
     }
}

{
      "fieldValues": [
        {
            "contact": "113",
            "field": "1",
            "value": "The Value for First Field",
            "cdate": "2020-08-01T10:54:59-05:00",
            "udate": "2020-08-01T14:13:34-05:00",
            "links": {
                "owner": "https://:account.api-us1.com/api/3/fieldValues/11797/owner",
                "field": "https://:account.api-us1.com/api/3/fieldValues/11797/field"
            },
            "id": "11797",
            "owner": "113"
        },
        {
            "contact": "113",
            "field": "6",
            "value": "2008-01-20",
            "cdate": "2020-08-01T10:54:59-05:00",
            "udate": "2020-08-01T14:13:34-05:00",
            "links": {
                "owner": "https://:account.api-us1.com/api/3/fieldValues/11798/owner",
                "field": "https://:account.api-us1.com/api/3/fieldValues/11798/field"
            },
            "id": "11798",
            "owner": "113"
        }
    ],
    "contact": {
        "email": "johndoe@example.com",
        "cdate": "2018-09-28T13:50:41-05:00",
        "udate": "2018-09-28T13:50:41-05:00",
        "orgid": "",
        "links": {
            "bounceLogs": "https://:account.api-us1.com/api/:version/contacts/113/bounceLogs",
            "contactAutomations": "https://:account.api-us1.com/api/:version/contacts/113/contactAutomations",
            "contactData": "https://:account.api-us1.com/api/:version/contacts/113/contactData",
            "contactGoals": "https://:account.api-us1.com/api/:version/contacts/113/contactGoals",
            "contactLists": "https://:account.api-us1.com/api/:version/contacts/113/contactLists",
            "contactLogs": "https://:account.api-us1.com/api/:version/contacts/113/contactLogs",
            "contactTags": "https://:account.api-us1.com/api/:version/contacts/113/contactTags",
            "contactDeals": "https://:account.api-us1.com/api/:version/contacts/113/contactDeals",
            "deals": "https://:account.api-us1.com/api/:version/contacts/113/deals",
            "fieldValues": "https://:account.api-us1.com/api/:version/contacts/113/fieldValues",
            "geoIps": "https://:account.api-us1.com/api/:version/contacts/113/geoIps",
            "notes": "https://:account.api-us1.com/api/:version/contacts/113/notes",
            "organization": "https://:account.api-us1.com/api/:version/contacts/113/organization",
            "plusAppend": "https://:account.api-us1.com/api/:version/contacts/113/plusAppend",
            "trackingLogs": "https://:account.api-us1.com/api/:version/contacts/113/trackingLogs",
            "scoreValues": "https://:account.api-us1.com/api/:version/contacts/113/scoreValues"
        },
        "id": "113",
        "organization": ""
    }
}