Getting error as "Class not Registered" in Delphi while using a c# dll

Question

I am trying to create a C# DLL which could be used in Delphi. But I am getting an error at implementation:

My C# code is follows:

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.Serialization.Json;
using System.Text;

namespace WebServiceHelper
{
    [Guid("4762FAC0-9CCC-4F9B-B1CD-E8C15FF13A02")]
    [ComVisible(true)]
    public interface IDataSync
    {
        int Add(int a, int b);
    }

    [Guid("DE887257-1A62-420C-BEED-BC6A73DF8F9D")]
    [ClassInterface(ClassInterfaceType.None)]
    [ComVisible(true)]
    public class DataSync : IDataSync
    {

        public int Add(int a, int b)
        {
            return a + b;
        }
    }
}

I have also checked the Registry for COM interop option in C# project:

Post build, I registered the DLL using regasm:

regasm.exe D:\path\WebServiceHelper.dll /tlb: "WebServiceHelper.tlb" /codebase

In Import Type Library, the .tlb or .dll file is not visible, so I added it from the Add option:

Delphi Code:

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Button1: TButton;
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses WebServiceHelper_TLB;

procedure TForm1.Button1Click(Sender: TObject);
var helper1 : TDataSync;
begin
  helper1:= TDataSync.Create(Self);
  writeln(helper1.Add(5,5));
  Edit3.Text := InttoStr(helper1.Add(5,5));
end;

end.