How to enable Toggle function in .Net Core Using Toggle Nuget Package function?

Below are the changes I made to my application. Added FeatureToggle package in code. And created a new print class (class class only) Extension SimpleFeatureToggle.

using FeatureToggle;

namespace AspDotNetCoreExample.Models
{
    public class Printing : SimpleFeatureToggle {}
}

      

        
        
        
      

    

appSettings.json added featureToggle Key and it is set to true. So the Printing class will read it and enable the toggle function.

    {
  "FeatureToggle": {
    "Printing": "true"
  }
  }       

      

        
        
        
      

    

** Startup.cs Registered my print service in the ConfigureServices method. I passed the config file (appSettings.json) to the print class. In the meantime, there is no need to worry about it. ”

   public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

    public IConfigurationRoot Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        // Set provider config so file is read from content root path
        var provider = new AppSettingsProvider { Configuration = Configuration };
        services.Configure<AppSettings(Configuration.GetSection("AppSettings"));
        services.AddSingleton(new Printing { ToggleValueProvider = provider });       
        services.AddTransient<IMapper, Mapper>();
        // Add framework services.
        services.AddMvc();
    }

      

        
        
        
      

    

// In the Mapper class to enable the toggle feature or not and to enable the features.

namespace STAR.Marketing.Portal.Web
{
    public class Mapper: Mapper
    {
        private readonly Printing _print;

        public Mapper(Printing print) //Dependency Injection to get Printing
        {
            _print = print;
        }
        public string Enabled()
        {
            return _print.FeatureEnabled;   // To check the feature is enabled but getting the Error System.FileIOException
        }
    }
}

      

        
        
        
      

    

What are the mistakes I made in the above code? Why am I getting this error in my code, System.FileIOException.?