I'm very new to NEST and Elasticsearch but at my workplace they asked me to produce a wpf client to search and retrieve documents from elasticsearch.

This is an example of what is stored in Elastic

{
    "_index" : "testing_devices",
    "_type" : "_doc",
    "_id" : "0o6ZeX8BRPRTU2ODedUM",
    "_score" : 1.0,
    "_source" : {
      "timestamp_Local" : "2022-03-11T16:29:34.5763990 01:00",
      "event" : "TestLog",
      "log" : {
        "Guid" : "d8bb9004-7cb1-4594-8c93-80135a8b736c",
        "SerialNumber" : "",
        "RecordType" : 0,
        "Operatore" : "Alessandro",
        "Name" : "03) Configurazione integrato USB FTDI",
        "Result" : 0,
        "StartDate" : "2022-03-11T16:14:42.3746145 01:00",
        "EndDate" : "2022-03-11T16:14:43.6001675 01:00"
      }
    }
  }

POCO

public class Log
{
    public string Guid { get; set; }
    public string SerialNumber { get; set; }
    public int RecordType { get; set; }
    public string Operatore { get; set; }
    public string Name { get; set; }
    public int Result { get; set; }
    public DateTime? StartDate { get; set; }
    public DateTime? EndDate { get; set; }
}

now my task is to search a document by Guid and so this is what i wrote in my client application just to test:

public partial class MainWindow : Window
{
    ElasticClient? client = new ElasticClient();
    ConnectionSettings? settings = new ConnectionSettings(new Uri("https://elk.xyz.to:9200")).DefaultMappingFor<Log>(i=>i.IndexName("testing_devices"))
        .DefaultIndex("testing_devices")
        .ApiKeyAuthentication("xxx", "yyy");

    public MainWindow()
    {
        InitializeComponent();
        client = new ElasticClient(settings);
        var result = client.Search<Log>(s => s.Index("testing_devices").Query(q => q.Match(m => m.Field(f => f.Guid).Query("d8bb9004-7cb1-4594-8c93-80135a8b736c"))));
    }
}

but no results are coming out of my query,it clearly say zero hits, as I already read a lot, without being able to produce any significant steps in order to achieve my goals, please can someone point me to the right direction?

EDIT: I'm adding the INDEX Definition for further investigations: