title: "registration_ids" field is not a JSON array (Firebase)
body: <p>I am facing problem with Firebase "registration_ids". When I send the request from Rest Client i get the successful response.</p>
  
  <pre><code>{"multicast_id":4650719213012935695,"success":2,"failure":0,"canonical_ids":0,"results":[{"message_id":"0:1468837777484579%214918aff9fd7ecd"},{"message_id":"0:1468837777484484%214918aff9fd7ecd"}]}
  </code></pre>
  
  <p>But when I call same php script from my Android application it gives me error in the response. (I got the response in Charles Proxy)</p>
  
  <pre><code>"registration_ids" field is not a JSON array
  </code></pre>
  
  <p>Here is my php script</p>
  
  <pre><code>function fetchFirebaseTokenUsers($message) {       
      $query = "SELECT token FROM firebase_tokens";
      $fcmRegIds = array();
      if($query_run = mysqli_query($this-&gt;con, $query)) {         
          while($query_row = mysqli_fetch_assoc($query_run)) {
              array_push($fcmRegIds, $query_row['token']);
          }
      }
  
      if(isset($fcmRegIds)) {
          $pushStatus = $this-&gt;sendPushNotification($fcmRegIds, $message);
      }
  }
  
  function sendPushNotification($registration_ids, $message) {
  
      ignore_user_abort();
      ob_start();
  
      $url = 'https://fcm.googleapis.com/fcm/send';
  
      $fields = array(
          'registration_ids' =&gt; $registration_ids,
          'data' =&gt; $message,
      );
  
      define('GOOGLE_API_KEY', 'AIzaSyC.......VdYCoD8A');
  
      $headers = array(
          'Authorization:key='.GOOGLE_API_KEY,
          'Content-Type: application/json'
      );      
  
      $ch = curl_init();
      curl_setopt($ch, CURLOPT_URL, $url);
      curl_setopt($ch, CURLOPT_POST, true);
      curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
      curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
      curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
  
      $result = curl_exec($ch);
      if($result === false)
          die('Curl failed ' . curl_error());
  
      curl_close($ch);
      return $result;
      ob_flush();
  }
  </code></pre>