Send Json from client application and receive on Server

I'm having a problem sending a json from my client application to my API on the server. The Json is generated correctly, and the POST request is performed, however on the server side the following error is reported:

"message": "Ocorreu um erro.",
"exceptionMessage": "Não é possível associar o parâmetro 'dados_json'. É preciso especificar um binder de modelo personalizado para associar parâmetros do tipo 'StringContent'.",
"exceptionType": "System.InvalidOperationException",
"stackTrace": "   em System.Web.Http.Controllers.HttpActionBinding.ExecuteBindingAsync(HttpActionContext actionContext, CancellationToken cancellationToken)\r\n   em System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__5.MoveNext()\r\n--- Fim do rastreamento de pilha do local anterior onde a exceção foi gerada ---\r\n   em System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   em System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   em System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__15.MoveNext()"

The sending code of the HttpPOST request that runs the client application is this:

 async void ExecuteSalvarCommand()
    {
        try
        {
            var stringDados = await Task.Run(() => JsonConvert.SerializeObject(data));
            var httpContent = new StringContent(stringDados, Encoding.UTF8, "application/json");

            using (var httpClient = new HttpClient())
            {

                // Do the actual request and await the response
                var httpResponse = await httpClient.PostAsync($"{ BaseUrl}salvar", httpContent);

                // If the response contains content we want to read it!
                if (httpResponse.IsSuccessStatusCode)
                {
                    await App.Current.MainPage.DisplayAlert("Tlab", "Dados cadastrados com sucesso!", "OK");
                    ClearXML();
                    NSerie = "";
                }
                else
                {
                    await App.Current.MainPage.DisplayAlert("Tlab", "Falha ao cadastrar dados, verifique sua conexão com a internet!", "OK");
                }
            }
        }

The code that receives the POST on the server is this:

 [HttpPost]
    [Route("salvar")]
    public HttpResponseMessage InsertorUpdate(StringContent dados_json)
    {
        if (Application.BD.Conectar())
            return Request.CreateResponse(HttpStatusCode.Created, Application.Querys.Insert(dados_json));
        else return Request.CreateResponse(HttpStatusCode.BadRequest, error);
    }

The object that receives the Json information sent by the client application is this:

    public class Relacao
{
    public int tap { get; set; }
    public double nominal { get; set; }
    public double medido { get; set; }
    public double ErroP { get; set; }
}

public class Identificador
{
    [JsonProperty("num_serie")]
    private string num_serie;

    [JsonProperty("condicao")]
    private string condicao;

    [JsonProperty("tipo_relacao")]
    private string tipo_rel;

    public string Tipo_rel { set => tipo_rel = value; }
    public string Condicao { set => condicao = value; }
    public string Num_serie { set => num_serie = value; }
}

//Gerar Json
public class Dados
{
    [JsonProperty("Identificador")]
    public Identificador identificador = new Identificador();

    [JsonProperty("objetos")]
    public ObservableCollection<Relacao> objetos { get; set; }
}