curl "https://app.tatango.com/api/v2/lists/<ID>/custom_field" -d '{"custom_field":{"label":"The Label","key":"the_key","content_type":"text","max_length":9999,"pattern":"[A-Za-z0-9]","should_validate_regex_via_api":false,"default_value":"The Default Value"}}' -X POST \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -u emailaddress@mydomain.com:my_api_key \
  -H "Host: example.org" \
  -H "Cookie: "

{
  "status": "OK",
  "custom_field": {
    "list_id": 30,
    "key": "the_key",
    "pattern": "[A-Za-z0-9]",
    "max_length": 9999,
    "default_value": "The Default Value",
    "can_insert": true,
    "can_segment": true,
    "created_at": "2023-11-22T08:14:19.000-08:00",
    "updated_at": "2023-11-22T08:14:19.000-08:00",
    "mask": null,
    "label": "The Label",
    "content_type": "text",
    "should_validate_regex_via_api": false
  }
}