使用 PHP 向 Android 设备发送推送通知

我正在尝试弄清楚如何使用 PHP 向 Android 设备发送推送通知。

我已在多个网站上查找过它，这是我最后一次尝试：

function sendFCM($registrationIds, $notifTitle, $notifDesc, $notifChannel, $data) {

    $client = new Google_Client();
    $client->setAuthConfig('bla.json');
    $client->addScope('https://www.googleapis.com/auth/firebase.messaging');
    $client->refreshTokenWithAssertion();
    $token = $client->getAccessToken();
    $accessToken = $token['access_token'];

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

    $notification = array
    (
        "title" => $notifTitle, 
        "body" => $notifDesc, 
        "icon" => "ic_logo_circle",
        "android_channel_id" => $notifChannel
    );

    $fields = array
    (
        'notification' => $notification, 
        'data' => $data, 
        'registration_ids' => $registrationIds
    );      

    $ch = curl_init();
    curl_setopt( $ch,CURLOPT_URL, 'https://fcm.googleapis.com/v1/projects/projectname/messages: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);
    print($result);

    curl_close($ch);
}

$notifData = array( 
    "title" => "this is the title",
    "msg" => "the desc",
    "image" => "whatever.jpg"
);

sendFCM($registrationIds, "Antwort auf Kommentar", "Cornholio hat dir geantwortet", "channel_reply_comment", $notifData);

$registrationIds包含多个 Android 设备令牌的数组

{ “错误”：{ “代码”：400，“消息”：“收到无效的 JSON 负载。未知名称“通知”：找不到字段。\ n收到无效的 JSON 负载。未知名称“数据”：找不到字段。\ n收到无效的 JSON 负载。未知名称“registration_ids”：找不到字段。“，”status“：“INVALID_ARGUMENT”，“详细信息”：[{“@type”：“type.googleapis.com/google.rpc.BadRequest”，“fieldViolations”：[{“描述”：“收到无效的 JSON 负载。未知名称“通知”：找不到字段。“}，{“描述”：“收到无效的 JSON 负载。未知名称“数据”：找不到字段。“}，{“描述”：“收到无效的 JSON 负载。未知名称“registration_ids”：找不到字段。“}]}]}