public Task<HttpResponseMessage> AddPaymentMethod(CancellationToken token, CreditCard creditCard, string environmentKey) { var uri = string.Format(ROOT_URL + "/payment_methods.xml?environment_key={0}", environmentKey); var xml = string.Format("<payment_method>{0}</payment_method>", creditCard.ToXml()); var request = new HttpRequestMessage(HttpMethod.Post, uri); var content = new StringContent(xml, null, "application/xml"); request.Content = content; return Client.SendAsync(LogRequest(request), HttpCompletionOption.ResponseContentRead, token); }