title: OneSignal error on postNotification
body: <p>I came back to some code I had been working on last year and updated everything, now my code isn't working. When I call post notification now I get "ERROR: Create notification failed"</p>
  
  <p>what I have is this in my AppDelegate:</p>
  
  <pre><code>OneSignal.initWithLaunchOptions(launchOptions, appId: "xxxxxx")
  </code></pre>
  
  <p>And here is my call to post:</p>
  
  <pre><code>let data = ["contents": ["en": "Push"], "include_player_ids": tokens] as [String : Any]
  
  OneSignal.postNotification(data)
  </code></pre>
  
  <p>When I make the above call, I've checked that tokens is equal to: </p>
  
  <p>["xxxxxxx"] where xxxxxx is a device token. Is there something I'm missing? I've checked that my version number for OneSignal is 2.3.4 and I've enabled the proper capabilities in my project settings. If no one knows what the problem is just from looking, is there a way to at least get more info from the error? Thank you</p>