PHP Firebase notification shows in tray but not popping up

Question

I am using php to send push notification using firebase to my Android app build using unity. App is receiving notification and showing it in a tray, but not showing it as pop up notification like whats app or other apps do.

My php code is:

function send_notification ($tokens, $message){
    $url = 'https://fcm.googleapis.com/fcm/send';
    $notification= array('title' => 'Winner!!','body' => $message);
    $data= array('custom_notification' => $custom_notification );
    $fields = array(
            'registration_ids' => $tokens,
            'notification' => $notification,
        );

    $headers = array(
        'Authorization:key = AAAA5C-Y_Ew:APA91bFD1g98n19DZD8FkaEYiME4tDsniePTKU1sGww1EAD7dtSKP6FEqlRGcTpB_MCD_7UM7ToWis1VnZO-dtDXMLFSZtaSIDAQ0fACbJ_SOFjWd93klckboahy3eZr93Z9M02LfP_s',
        '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_RETURNTRANSFER, true);
   curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0);  
   curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
   curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
   $result = curl_exec($ch);           
   if ($result === FALSE) {
       die('Curl failed: ' . curl_error($ch));
   }
   curl_close($ch);
   return $result;
}

it also showing gray scaled icon instead of colored icon. I want to show notification as pop up. is there anyway to do so using FCM?

Answer 1

Instead of 'notification' => $notification use only data key while sending notification for android only.

iOS require only 'notification' => $notification however.