var client = new RestClient("url");
client.Timeout = -1;
var request = new RestRequest(
Method.POST);
request.AddHeader("X-Atlassian-Token", "no-check");
request.AddHeader("Authorization", "Basic c2VraXNvdjoyODY1MTQ=");
request.AddFile("file", "/C:/Users/admin/Desktop/avatar.jpg");
IRestResponse response = client.Execute(request);
Console.WriteLine(response.Content);
Для будущих поколений)