One or more validation errors occurred in a get request with Basic Authentication authorization

I am working with basic authentication in a get request, and it takes parameters, but it throws the following error as a status code and response body.

{"type":"https://tools.ietf.org/html/rfc7231#section-6.5.1","title":"One or more validation errors occurred.","status":400,"traceId":"00-5bebf6cfcb0e1cec5306c5dbff1cf6c0-c432aba0a422c830-00","errors":{"password":["The password field is required."],"user_name":["The user_name field is required."]}}.

I don't know what it means and what should I fix in my code. Can anybody help me, here is my code:

String basicAuth =
            'Basic ${base64.encode(utf8.encode('$_email:$encodedPassword'))}';

var queryParams = {
          'domain_name': 'domainName',
          'token': 12345.toString(),
        };
   final uri =
            Uri.https(baseUrl, '/api/Employee/validate_user', queryParams);

        final res = await http.get(uri, headers: {
          HttpHeaders.contentTypeHeader: 'application/json',
          HttpHeaders.authorizationHeader: basicAuth,
        });
        if (res.statusCode == 200) {

         debugPrint(res.body);

           }else {
          debugPrint("Status " + res.statusCode.toString());
          debugPrint(res.body);
        }