$fcmNotification = [
'priority'=>'high',
"content_available"=> true,
"mutable_content"=> true, //if you want to modify notification layout
'to' => '/topics/ios_topic',
"notification" => array(
"body" => "Body text",
"title" => "Title Text",
"subtitle" => "Sub title text",
'sound' => 'default',
'badge' => '0'
)
];