PHP json_encode to C# Object unable to convert

I have this array of objects that contains some strings and an array of strings that I want to return from my server:

"[{"original_file_name":"Plain_HAIR.pdf","encrypted_file_name":"UTTSJG13V1EC46J.pdf","is_successful":true,"message":"","email":"[\"[email protected]\"]","doctype":"HAIR"}]"

On my local app, I have a class that looks like this:

public class FileUploadResultViewModel
{
    public string original_file_name { get; set; }
    public string encrypted_file_name { get; set; }
    public string is_successful { get; set; }
    public string message { get; set; }
    public string email { get; set; }
    public string doctype { get; set; }
}

if (res.StatusCode == System.Net.HttpStatusCode.OK)
{
    return JsonConvert.DeserializeObject<List<FileUploadResultViewModel>>(res.Content);
}
else
{
    return null;
}

The issue is that when it comes back to the local app, I get an error saying :

{"Error converting value "[{"original_file_name":"Plain_HAIR.pdf","encrypted_file_name":"UTTSJG13V1EC46J.pdf","is_successful":true,"message":"","email":"["[email protected]"]","doctype":"HAIR"}]" to type 'System.Collections.Generic.List`1[Uploader.ViewModels.FileUploadResultViewModel]'. Path '', line 1, position 1521."}

Am I converting it wrongly or are there some steps missing?

EDIT:

This is how I define the object on the server:

$object = (object) [
    'original_file_name' => $item["original_file_name"],
    'encrypted_file_name' => $item["file_name"],
    'is_successful' => true,
    'message' => '',
    'email' => NULL,
    'doctype' => $item["doctype"]
];
array_push($myArray, $object);
$this->response(json_encode($myArray));

EDIT 2: Showing the method to retrieve the json result

public FileUploadResultViewModel Upload(List<FileUploadViewModel> sdvm)
{
    var js = JsonConvert.SerializeObject(sdvm);
    RestClient client = new RestClient();
    var link = url;
    var username = username;
    var password = password;
    client.BaseUrl = new Uri(link);
    client.Authenticator = new HttpBasicAuthenticator(username, password);
    RestRequest request = new RestRequest();
    request.AddJsonBody(sdvm);
    request.Method = Method.POST;
    var res = client.Execute(request);
    if (res.StatusCode == System.Net.HttpStatusCode.OK)
    {
        return JsonConvert.DeserializeObject<FileUploadResultViewModel>(res.Content);
    }
    else
    {
        return null;
    }
}