Error generating file

I have a method that generates a file, this method is actually generating the file, I have another method inside my service that returns the file for download and for this I return a List until then I return that list with bytes for my controler as follows. Controller Call

    public JsonResult RetornaDownloadExcel(Guid GuidExcel)
    {
        var retorno = 
    JsonServiceHelper.GimmeInstance().ExecuteArray("http://localhost:1234/", 
    "/SNService/RetornaDownloadExcel", GuidExcel, true);

        List<Byte> Bytes = retorno.Value.ToObject<List<Byte>>();

        var base64 = Convert.ToBase64String(Bytes.ToArray());
        var fileSrc = String.Format("data:application/vnd.ms-excel;base64,{0}", base64);

        return Json(new { Bytes });
    }

that refers to this call.

    public List<Byte> RetornaDownloadExcel(Guid GuidExcel)
    {

        List<Byte> Bytes = new List<Byte>();
        String fullpath = "C:/Relatorio/Sns/" + GuidExcel + ".xls";

        if (File.Exists(fullpath))
        {
            StreamReader sr = new StreamReader(fullpath);

            MemoryStream ms = new MemoryStream();

            sr.BaseStream.CopyTo(ms);


            foreach (var Byte in ms.ToArray())
            {
                Bytes.Add(Convert.ToByte(Byte));
            }
        }

        return Bytes;
    }

and to call the controller I have a js with the following code

    function RetornaDownloadExcel() {
    jQuery.ajaxSettings.traditional = true;
    $.ajax({
        type: "POST",
        url: '/SN/RetornaDownloadExcel',
        data: { GuidExcel: guidexcel },
        success: function (data) {
            a = document.createElement('a');
            document.body.appendChild(a);
            var byteArray = new Uint8Array(data.Bytes);
            blob = new Blob([byteArray], { type: 'application/vnd.ms-excel' 
    });
            url = window.URL.createObjectURL(blob);
            a.href = url;
            a.download = "Sns.xls";
            a.click();
            window.URL.revokeObjectURL(url);
            document.body.removeChild(a);
        },
        error: function (xhr, status, error) {


        }
    });
};

But I can not download the excel file I think I'm missing something on the controller, can you help me with my error?

Thank you.