Ajax with AntiForgeryToken does not pass data

I'm having trouble putting AntiForgeryToken on my date from json . Here is the code that I pass the information of my data to controller without problems.

 var todos_servicos = {
        ServicoFornecedor,
        ServicoDesabilitado: $("#ServicoDesabilitado").val(),
        CodigoInterno: $("#CodigoInterno").val(),
        Descricao: $("#Descricao").val(),
        Observacoes: $("#Observacoes").val()
    };

    $.ajax({
        url: '/ServicosTerceiros/SalvarServicos', 
        dataType: "json", 
        type: "POST",
        contentType: 'application/json; charset=utf-8',
        cache: false, 
        data: JSON.stringify(todos_servicos), // passar os parametros
        success: function (data) {

To recover the AntiForgeryToken I did so:

<script type="text/javascript">
function gettoken() {
    var token = '@Html.AntiForgeryToken()';
    token = $(token).val();
    return token;
}

Now when I use the date to send token it gives me the following error:

  

"Failed to load resource: the server responded to a status of 500   (Internal Server Error) "

I've made several attempts on my date, follow them:

  var jsonString = JSON.stringify(todos_servicos);
    $.ajax({
        url: '/ServicosTerceiros/SalvarServicos', 
        dataType: "json",
        type: "POST", 
        contentType: 'application/json; charset=utf-8', 
        cache: false, 
        data: { __RequestVerificationToken: gettoken(), jsonString }, // passar os parametros
        success: function (data) {

In my controller :

[ValidateAntiForgeryToken]
[HttpPost]
public ActionResult SalvarServicos(DTO.ServicosTerceiros jsonString)
{
    // codigo
}

Declaration in view:

@Html.AntiForgeryToken()
@Html.ValidationSummary(true, "", new { @class = "text-danger" })