title: Firebase notifications - subscribing to topics using iOS FCM token failing all the time... using C# API
body: <p>I have an App - Android and iOS with a partial web view.</p>
  
  <p>I'm using a C# API back end and notifications via Firebase Cloud messaging works fine for Android, especially subscribing and unsubscribing to topics using the "registered" FM token.</p>
  
  <p>Every time I try to subscribe to a topic using a FCM token that comes from an iOS device it fails.</p>
  
  <p>I'm using very simple code to add tokens to topics e.g. </p>
  
  <p>using (var httpRequest = new HttpRequestMessage(HttpMethod.Post, "<a href="https://iid.googleapis.com/iid/v1/" rel="nofollow noreferrer">https://iid.googleapis.com/iid/v1/</a>" + [fcmToken] + "/rel/topics/" + [topic name]))
  {</p>
  
  <pre><code>httpRequest.Headers.TryAddWithoutValidation("Authorization", [server key]);
  httpRequest.Headers.TryAddWithoutValidation("Sender", [sender id]);
  httpRequest.Content = new StringContent(jsonBody, Encoding.UTF8, "application/json");
  
  using (var httpClient = new HttpClient())
  {
      var result = await httpClient.SendAsync(httpRequest);
      if (result.IsSuccessStatusCode)
      {
          //success
      }
      else
      {
         //failed
      }
  }
  </code></pre>
  
  <p>}</p>
  
  <p>Has anyone had any experience like this or a solution that I'm missing as to why iOS tokens are not getting subscribed to topics?</p>