title: FCM Android Notification sound issue
body: <p>I am trying to send notification using php to Android Application, and which is working fine without sound. I am receiving the notification both foreground and background as expected. </p>
  
  <p>Here is the PHP code, </p>
  
  <pre><code>&lt;?php
  
  
  $token = $_GET['token'];
  $action = $_GET['action'];
  $msgTitle = $_GET['msgTitle'];
  $msgDescription = $_GET['msgDescription'];
  $notificationTitle = $_GET['notificationTitle'];
  
  
  require './google-api-php-client-2.2.2/vendor/autoload.php';
  $client = new Google_Client();
  $client-&gt;useApplicationDefaultCredentials(); 
  $client-&gt;setAuthConfig('./testPrjoectAPP-firebase-adminsdk-9hn21-22c1b3f426.json');
  $client-&gt;addScope('https://www.googleapis.com/auth/firebase.messaging');
  $httpClient = $client-&gt;authorize();
  $project = "testPrjoectAPP";
  $message = [
      "message" =&gt; [
          "notification" =&gt; [
              "body"  =&gt; "Message FCM",
              "title" =&gt; $notificationTitle
          ],
          "token" =&gt; $token,
  
         "data" =&gt; [
                  "action" =&gt; $action,
              "msgTitle" =&gt; $msgTitle,
              "msgDescription" =&gt; $msgDescription 
           ]
  
  
      ]
  ];
  $response = $httpClient-&gt;post("https://fcm.googleapis.com/v1/projects/{$project}/messages:send", ['json' =&gt; $message]);
  echo$response-&gt;getReasonPhrase(); // OK
  
  ?&gt;
  </code></pre>
  
  <p>But when I add sound parameter to notification payload and execute php I am getting <code>Bad Request</code> error from php. 
  .</p>
  
  <pre><code>$message = [
      "message" =&gt; [
          "notification" =&gt; [
              "body"  =&gt; "Message FCM",
              "title" =&gt; $notificationTitle,
              "sound" =&gt; "default"    
          ],
          // Send with token is not working
          "token" =&gt; $token,
  
         "data" =&gt; [
              "action" =&gt; $action,
              "msgTitle" =&gt; $msgTitle,
              "msgDescription" =&gt; $msgDescription
           ]
  
  
      ]
  ];
  </code></pre>
  
  <p><strong>Edit</strong> </p>
  
  <p>Here is the error message I got while printing with </p>
  
  <pre><code>data: "{\n \"error\": {\n \"code\": 400,\n \"message\": \"Invalid JSON payload received. Unknown name \\\"sound\\\" at 'message.notification': Cannot find field.\",\n \"status\": \"INVALID_ARGUMENT\",\n \"details\": [\n {\n \"@type\": \"type.googleapis.com/google.rpc.BadRequest\",\n \"fieldViolations\": [\n {\n \"field\": \"message.notification\",\n \"description\": \"Invalid JSON payload received. Unknown name \\\"sound\\\" at 'message.notification': Cannot find field.\"\n }\n ]\n }\n ]\n }\n}\n"
  </code></pre>