var result = _onlinePayment.Request(Gateways.Mellat, 123, 25000, "http://www.mywebsite.com/foo/bar/");

var result = _onlinePayment.Request(invoice =>
{
    invoice
          .UseAutoIncrementTrackingNumber()
          .SetAmount(25000)
          .SetCallbackUrl("http://www.mywebsite.com/foo/bar/")
          .UseGateway(Gateways.Mellat);
});

var result = _onlinePayment.Request(invoice =>
{
    invoice
          .UseAutoRandomTrackingNumber()
          .SetAmount(25000)
          .SetCallbackUrl("http://www.mywebsite.com/foo/bar/")
          .UseGateway(Gateways.Mellat);
});

var result = _onlinePayment.Request(invoice =>
{
    invoice
          .UseTrackingNumberProvider<MyTrackingNumberProvider>()
          //  یا 
          .UseTrackingNumberProvider(new MyTrackingNumberProvider())
          //  یا 
          .UseTrackingNumberProvider(services => new MyTrackingNumberProvider())
});

var result = _onlinePayment.Request(Gateways.ParbadVirtualGateway, 123, 25000, "http://www.mywebsite.com/foo/bar/");

services.AddParbad()
        .ConfigureGateways(gateways =>
        {
            gateways
               .AddMellat()
               .WithOptions(options => 
               {
                    options.TerminalId = 123;
                    options.UserName = "abc";
                    options.UserPassword = "xyz;
               )
               .WithProxy(new Uri("Proxy Server URL"), "UserName", "Password");
        });

public class MyTokenProvider : IPaymentTokenProvider
{
    public Task<string> ProvideTokenAsync(Invoice invoice, CancellationToken cancellationToken = new CancellationToken())
    {
        // تولید و برگرداندن توکن در اینجا
    }

    public Task<string> RetrieveTokenAsync(CancellationToken cancellationToken = new CancellationToken())
    {
        // خواندن و برگرداندن توکن در اینجا
    }
}