JsonUtility can't deserialize complex classes

Getting Started
1

I’m trying to use JsonUtility to deserialize a list of objects but I keep getting this error:
JSON must represent an object type.

I’ve tries using LitJson.JsonMapper as well, the error I get then is:
The value passed in must be an enum base or an underlying type for an enum, such as an Int32.\r\nParameter name: value

What am I doing wrong?

The code:

var stateDetails = new List<StateDetails>();
stateDetails = JsonUtility.FromJson<List<StateDetails>>(jsonString);

 [Serializable]
    public class StateDetails
    {
        public string Text { get; set; }
        public States State { get; set; }
        public List<Transition> Transitions { get; set; }
    }

[Serializable]
    public class Transition
    {
        public KeyCode KeyCode { get; set; }
        public States State { get; set; }
    }

[Serializable]
    public enum States
    {
        room_0,
        room_1,
        room_2
    };

jsonString:

[
    {
        "Text": "Sample text.",
        "State": 0,
        "Transitions":
        [
            {"KeyCode": "S", "State": 2},
            {"KeyCode": "M", "State": 1}
        ]
    },
    {
        "Text": "Sample text.",
        "State": 2,
        "Transitions":
        [
            {"KeyCode": "R", "State" : 0}
        ]
    }
]
2

How are you generating the JSON? I find you get better results if you generate it from JsonUtility as well. At least to get the initial template.