Inheritance: SteamWebRequest
 public async Task<Cart> IsValidCartAsync(long steamId, long cartId)
 {
     SteamMicroTransaction steamMicroTransaction = new SteamMicroTransaction(this.developerKey);
     return await steamMicroTransaction.IsValidCartAsync(steamId, cartId);
 }
 public async Task<Cart> CreateCartAsync(long steamId)
 {
     SteamMicroTransaction steamMicroTransaction = new SteamMicroTransaction(this.developerKey);
     return await steamMicroTransaction.CreateCartAsync(steamId);
 }