How to solve: incompatible types "TJSONIterator" and "string"

Following the Readers and Writers JSON Framework (which reduces memory consumption), I tried to use a RESTful service to get data via HTTP.

But I get an error :

E2010 Incompatible types: 'TJSONIterator' and 'string'

on the line:

LJRates := LJIter.AsDouble.ToString;

Async.Run<TStringList>(function: TStringList
    var
      LHTTP: THTTPClient;
      LResp: IHTTPResponse;
      LJIter: TJSONIterator;
      LJRates: TJSONIterator;
      LJTextR: TJsonTextReader;
      LStrR: TStringReader;
//      LResult: Boolean;
      I: Integer;
    begin
      LHTTP := THTTPClient.Create;
      try
        LResp := LHTTP.Get('http://api.fixer.io/latest');

        {$REGION 'check for errors'}
        if LResp.StatusCode = 200 then
        begin
//          LResult := not LResp.ContentAsString(TEncoding.UTF8).IsEmpty
          // or
//          LStrR := TJSONObject.ParseJSONValue(LResp.ContentAsString(TEncoding.UTF8)) as TJSONObject;
          // or
//        LStrR := LResp.ContentAsString(TEncoding.UTF8);
          // or
          LStrR := TStringReader.Create(LResp.ContentAsString(TEncoding.UTF8));
        end  else
        begin
          raise Exception.CreateFmt('Cannot get rates. HTTP %d - %s', [LResp.StatusCode, LResp.StatusText]);
        end;
        {$ENDREGION}

        LJTextR := TJsonTextReader.Create(LStrR);
        LJIter := TJSONIterator.Create(LJTextR);
        try
          // gets the json object 'rates' and
          LJIter.Recurse; // prepare to enter object
          while LJIter.Next do;
          begin
            LJIter.Recurse; // enter object
            LJIter.Next('rates');
            LJRates := LJIter.AsDouble.ToString;
            Result := TStringList.Create;
            // loop through the property names
            for I := 0 to LJRates.Depth - 1 do
            begin
              //add each names in the resulting TStringList
              Result.Add(LJRates.Path[I]);
            end;
            Result.Sort;
          end;
        finally
          LJIter.Free;
        end;
      finally
        LHTTP.Free;
      end;
    end,

What is the correct way to iterates through the JSON, reading the content, and displaying the rate values?