title: OneSignal Chrome multiple notification
body: <p>I have some problem with web push notification.
  I'm able to send the notification regularly, but, when I send two notification and the first is still visible on the screen, the second overwrite the first one.</p>
  
  <p>The REST API is called by an MVC site written with C#, the object I send is the following:</p>
  
  <pre><code>var obj = new
          {
              app_id = _appKey,
              contents = new { en = message },
              headings = new { en = title },
              included_segments = new[] { "All" },
              url,
              chrome_web_icon = imageUrl,
              priority = 1,
              id = DateTime.Now.ToString("yyyyMMddHHmmss")
          };
  </code></pre>
  
  <p>Did anyone experienced the same issue? 
  How can I solve that?</p>