How to display a list of strings from a JSON file in a datagrid?

Object Class:

public class SIReport
    public string Sortcode { get; set; }
    public string Incident { get; set; }

public class Message
    public bool IsSIR { get; set; }
    public string Header { get; set; }
    public string Subject { get; set; }
    public List<string> Hashtags { get; set; }
    public List<string> URLs { get; set; }
    public SIReport SIReport { get; set; } 


I start by reading in a text file as a JSON

string jsonData = File.ReadAllText(@"C:\text.txt");

var messageList = JsonConvert.DeserializeObject<List<Message>>(jsonData);

The file looks like this:

  "IsSIR": true,
  "Header": "E123456789",
  "Subject": "SIR Subject Line",
  "Hashtags": [
  "URLs": [
  "SIReport": {
    "Sortcode": "98-23-43",
    "Incident": "N/A"

Then I simply bind the list to the ItemsSource

Datagrid_Msg.ItemsSource = messageList;

It displays the strings no problem but under the columns with Lists it just displays "(Collection)". How do i go about displaying those lists of strings?