Dead-simple license key validation using Keygen (https://keygen.sh)

licensing.cs

using RestSharp;
using System;
using System.Collections.Generic;

public class Example
{
  // This is your Keygen account ID or slug.
  //
  // Available at: https://app.keygen.sh/settings
  const string KEYGEN_ACCOUNT_ID = "YOUR_KEYGEN_ACCOUNT_ID";
  
  public static void Main()
  {
    var keygen = new RestClient(string.Format("https://api.keygen.sh/v1/accounts/{0}", KEYGEN_ACCOUNT_ID));
    var request = new RestRequest("licenses/actions/validate-key", Method.POST);

    request.AddHeader("Content-Type", "application/vnd.api+json");
    request.AddHeader("Accept", "application/vnd.api+json");
    request.AddJsonBody(new {
      // Update this variable with a license key obtained from the current user.
      meta = new { key = "XXXX-XXXX-XXXX-XXXX" }
    });

    var response = keygen.Execute<Dictionary<string, object>>(request).Data;
    if (response.ContainsKey("errors"))
    {
      Console.WriteLine("Failed to validate license: {0}", response["errors"]);
      return;
    }
    var license = (Dictionary<string, object>) response["data"];
    var meta = (Dictionary<string, object>) response["meta"];

    if ((bool) meta["valid"])
    {
      // … do something with the valid license
    }
    else
    {
      // … do something else
    }
  }
}