Sort on Elastic Search .NET API

Elastic Stack Elasticsearch
1

can anyone pls share object initializer syntax for sort requests instead of lambdas?

i tried couple of things but they are not working

Code:

Dim req = New SearchRequest(Of testIndex)(txtIndex2.Text.Trim) With {
     .Query = New TermQuery("user") With {.Value = txtUserName.Text.Trim},
     .Sort = New List(Of ISort) From {
         New FieldSort With {
         .Field = "startedOn",
         .Order = SortOrder.Ascending
     }
 }

Error:

Severity Code Description Project File Line Suppression State
Error (active) BC30002 Type 'ISort' is not defined. ES.aspx.vb 41
Severity Code Description Project File Line Suppression State
Error (active) BC30456 'Field' is not a member of 'FieldSort'. ES.aspx.vb 43
Severity Code Description Project File Line Suppression State
Error (active) BC30456 'Ascending' is not a member of 'SortOrder'. ES.aspx.vb 44