SPO_AppOnly_SPAuth.cs

using Microsoft.SharePoint.Client;
using OfficeDevPnP.Core;
using System;

namespace AppPermissionsDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            string siteUrl = "https://yourtenant.sharepoint.com/sites/yoursite/";
            
            //Client id and Client secret created through appregnew.aspx and permissions granted through appinv.aspx
            string clientId = "<client-id>"; //e.g. 15107f17-5230-422b-873c-b3846211cba7
            string clientSecret = "<client-secret>"; //e.g. XeGMHUxRPOg0o1LeKqfWVYTzO0blGfXBPKvNiCQwHtc=

            var authManager = new AuthenticationManager();

            //PnP Core method
            ClientContext clientContext = authManager.GetAppOnlyAuthenticatedContext(siteUrl, clientId, clientSecret);

            Web web = clientContext.Web;
            clientContext.Load(web);
            clientContext.ExecuteQueryRetry();

            Console.WriteLine(web.Title);
        }

    }
}

Hi I am using above code but getting below error.
System.TypeInitializationException: The type initializer for 'OfficeDevPnP.Core.Utilities.TokenHelper' threw an exception.
---> System.TypeLoadException: Could not load type 'System.Web.Configuration.WebConfigurationManager' from assembly 'System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
at OfficeDevPnP.Core.Utilities.TokenHelper..cctor()