Additional Fields : Specify any additional fields that should be created with this contact as JSON. See the docs (https://developer.close.com/resources/contacts/#create-a-new-contact) for available fields. (example: "{
"custom.cf_FSYEbxYJFsnY9tN1OTAPIF33j7Sw5Lb7Eawll7JzoNh": "Account Executive",
}")