Example of creating an issue with attachment on Jira using Restsharp

CreateIssueWithAttachmentJiraUsingRestsharp.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using Jira
using RestSharp;
using RestSharp.Authenticators;

namespace Jira
{
    class Program
    {
      static void Main(string[] args)
      {
        var client = new RestClient("http://{URL}/rest/api/2");
        var request = new RestRequest("issue/", Method.POST);
  
        client.Authenticator = new HttpBasicAuthenticator("user", "pass");
        
        var issue = new Issue
        {
            fields =
                new Fields
                {
                    description = "Issue Description",
                    summary = "Issue Summary",
                    project = new Project { key = "KEY" }, 
                    issuetype = new IssueType { name = "ISSUE_TYPE_NAME" }
                }
        };
        
        request.AddJsonBody(issue);
        
        var res = client.Execute<Issue>(request);
        
        if (res.StatusCode == HttpStatusCode.Created)
        {
            Console.WriteLine("Issue: {0} successfully created", res.Data.key);
            
            #region Attachment            
            request = new RestRequest(string.Format("issue/{0}/attachments", res.Data.key), Method.POST);
                        
            request.AddHeader("X-Atlassian-Token", "nocheck");
            
            var file = File.ReadAllBytes(@"C:\FB_IMG_1445253679378.jpg");

            request.AddHeader("Content-Type", "multipart/form-data");
            request.AddFileBytes("file", file, "FB_IMG_1445253679378.jpg", "application/octet-stream");
            
            var res2 = client.Execute(request);

            Console.WriteLine(res2.StatusCode == HttpStatusCode.OK ? "Attachment added!" : res2.Content);
            #endregion
        }
        else
            Console.WriteLine(res.Content);
      }
    }
    
    public class Issue
    {
        public string id { get; set; }
        public string key { get; set; }
        public Fields fields { get; set; }
    }
    
    public class Fields
    {
        public Project project { get; set; }
        public IssueType issuetype { get; set; }
        public string summary { get; set; }
        public string description { get; set; }        
    }
    
    public class Project
    {
        public string id { get; set; }
        public string key { get; set; }
    }
    
    public class IssueType
    {
        public string id { get; set; }
        public string name { get; set; }
    }
}

Thank you for this, linked in from StackOverflow.