Invoke C# code in UiPath

Hi Guys,
I want to invoke below C# code in UiPath

var client = new RestClient(“”);
client.Timeout = -1;
var request = new RestRequest(Method.PUT);
request.AddHeader(“Content-Type”, “multipart/form-data”);
request.AddHeader(“Authorization”, “Basic authCode”);
request.AddFile(“attachments”, “/D:/Attachments/test.png”);
IRestResponse response = client.Execute(request);

But I am getting a few errors

I have added the RestSharp package to my project. Am I missing something?