I'm trying to setup a server to send push notifications.

I'm trying to send push notification toward user of an specified package e.g. something like `com.mysite.android` (This options is available in Firebase console).
Checking answers like [this](https://stackoverflow.com/a/38915623/1080355) I could not understand how to set `to` parameter to send push notifications to user of an specified package. I can find sample which send notification to `specific devices by their ids` or `news topics`.

**Clarification:** I'm the owner of application which I want sent push notifications.

If it helps here is my code:

```
<?php
    /*  
    Parameter Example
        $data = array('post_id'=>'12345','post_title'=>'A Blog post');
        $target = 'single tocken id or topic name';
        or
        $target = array('token1','token2','...'); // up to 1000 in one request
    */

        echo "Start<br/>";
        $result = sendMessage('{"id":"hello"}',null);
        var_dump($result);

        function sendMessage($data,$target){
            //FCM api URL
            $url = 'https://fcm.googleapis.com/fcm/send';
            //api_key available in Firebase Console -> Project Settings -> CLOUD MESSAGING -> Server key
            $server_key = 'xxxxxxxxxxxxxxxxxxxkeyxxxxxxxxxxxxxxxxxxxxxxxx';

            $fields = array();
            $fields['data'] = $data;
            $fields['restricted_package_name']='com.mysite.android ';
            $fields['dry_run']=true;

            if (isset($target)){
                if(is_array($target)){
                    $fields['registration_ids'] = $target;
                }else{
                    $fields['to'] = $target;
                }
            }
            //header with content_type api key
            $headers = array(
                'Content-Type:application/json',
                'Authorization:key='.$server_key
                );

            $ch = curl_init();
            curl_setopt($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 ($result === FALSE) {
                die('FCM Send Error: ' . curl_error($ch));
            }
            curl_close($ch);
            return $result;
        }

        ?>

```

Notice: I removed my `server_key` intentionally.