使用Firebase Console可以根据应用程序包向所有用户发送消息。但对于CURL或PHP API，这是不可能的。

通过API可以向指定的设备ID或订阅的用户发送通知给选定的主题或订阅的主题用户。

Get a view on following link. It will help you.
https://firebase.google.com/docs/cloud-messaging/send-message

例如，您可以使用用于谷歌云消息传递(GCM)的PHP脚本。Firebase及其控制台位于GCM之上。

我在github上找到了这个: https://gist.github.com/prime31/5675017

提示:这个PHP脚本会产生一个android通知。

因此:如果你想在Android中接收和显示通知，请阅读来自Koot的回答。

使用服务api。

URL: https://fcm.googleapis.com/fcm/send

方法类型:POST

标题:

Content-Type: application/json
Authorization: key=your api key

车身/有效载荷：

{
   "notification": {
      "title": "Your Title",
      "text": "Your Text",
      "click_action": "OPEN_ACTIVITY_1"
   },
   "data": {
      "<some_key>": "<some_value>"
   },
   "to": "<device_token>"
}

在你的应用程序中，你可以添加以下代码在你的活动中被调用:

<intent-filter>
    <action android:name="OPEN_ACTIVITY_1" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>

也检查答案在Firebase onmessagerreceived未调用时，应用程序在后台

Go to cloud Messaging select:  Server key



function sendGCM($message, $deviceToken) {

    $url = 'https://fcm.googleapis.com/fcm/send';
    $fields = array (
            'registration_ids' => array (
                $id
            ),
            'data' => array (
                "title" =>  "Notification title",
                "body" =>  $message,
            )
    );
    $fields = json_encode ( $fields );
    $headers = array (
        'Authorization: key=' . "YOUR_SERVER_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_RETURNTRANSFER, true );
    curl_setopt ( $ch, CURLOPT_POSTFIELDS, $fields );
    $result = curl_exec ( $ch );
    echo $result;

    curl_close ($ch);
}

或者你可以使用Firebase的云功能，对我来说，这是实现推送通知的更简单的方法。 重火力点/ functions-samples

下面是我使用CURL的项目中的工作代码。

<?PHP
//Avoid keys confusions!
//firebase Cloud Messaging have 3 different keys: 
//API_KEY, SERVER_KEY and PUSH_KEY ... here we need SERVER_KEY

// SERVER access key from Google firebase Console    
define( 'SERVER_ACCESS_KEY', 'YOUR-SERVER-ACCESS-KEY-GOES-HERE' );


 $registrationIds = array( $_GET['id'] );

  // prep the bundle
 $msg = array
 (
   'message'    => 'here is a message. message',
    'title'     => 'This is a title. title',
    'subtitle'  => 'This is a subtitle. subtitle',
    'tickerText'    => 'Ticker text here...Ticker text here...Ticker text here',
    'vibrate'   => 1,
    'sound'     => 1,
    'largeIcon' => 'large_icon',
    'smallIcon' => 'small_icon'
 );

 $fields = array
 (
    // use this to method if want to send to topics
    // 'to' => 'topics/all'
    'registration_ids'  => $registrationIds,
     'notification'         => $msg
 );

 $headers = array
 (
    'Authorization: key=' . SERVER_ACCESS_KEY,
    'Content-Type: application/json'
 );

 $ch = curl_init();
 curl_setopt( $ch,CURLOPT_URL, 'https://fcm.googleapis.com/fcm/send' );
 curl_setopt( $ch,CURLOPT_POST, true );
 curl_setopt( $ch,CURLOPT_HTTPHEADER, $headers );
 curl_setopt( $ch,CURLOPT_RETURNTRANSFER, true );
 curl_setopt( $ch,CURLOPT_SSL_VERIFYPEER, false );
 curl_setopt( $ch,CURLOPT_POSTFIELDS, json_encode( $fields ) );
 $result = curl_exec($ch );
 curl_close( $ch );

 echo $result;