start field should be marked as requeired, without this field got error:
"message": "You entered invalid value for field : [start]. Values that represent [start] can't be null and can't be empty. Please make sure that the [start] date is not greater than 9999-12-31 and not less than 0001-01-01. Ensure that the [start] date is in following format: \"yyyy-MM-ddThh:mm:ssZ\" Example: 2018-11-29T13:00:46Z.",