Variable in CURL

Hi, I am using Firebase notification below is my CURL code I am calling this function on order status change.

 $order_id = 123;
 $order_status = "pending";
 if($order->save()){
        $curl = curl_init();
curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://fcm.googleapis.com/fcm/send',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS =>'{
 "to" : "e7Oeb3OAXUmMry4gP0LxFP:APA91bHKwTT2TpWxAJY17lxtvIjg_eYOlOLgkVPnrgAf9cmDsiFV6-Kz3BTl1DipDDJGhA8sFbnaUaGeajIunY6hsCjsu-q8xpssU8z8VgXnhlLOnpZPVmZ-SyalO-h4M4RCKcDhjQS7",
"data" : {
        "title":"Android",
        "order_id" :1,
        "order_status" :"pending", 
},

}',
  CURLOPT_HTTPHEADER => array(
    'Authorization: key=AAAAfexbmoo:APA91bE5VzPqQqF_U1CIgYTV2mk_q-SmW6veR4w1pF2IYH6Jw1WoFqsQ8VN7mQcJOqyaAinByslgyvSy8JDABeXCuyn1rNegjk8MTwEFck97uaf1AD9aBFPQdsNVkbFExdKeON6VaYyp',
    'Content-Type: application/json'
  ),
));

Things are working fine on static data. If I use dynamic values in data collection then notifications are not working Please help me to fix this :)