Works in 2020
$response = Http::withHeaders([
'Content-Type' => 'application/json',
'Authorization'=> 'key='. $token,
])->post($url, [
'notification' => [
'body' => $request->summary,
'title' => $request->title,
'image' => 'http://'.request()->getHttpHost().$path,
],
'priority'=> 'high',
'data' => [
'click_action'=> 'FLUTTER_NOTIFICATION_CLICK',
'status'=> 'done',
],
'to' => '/topics/all'
]);