Push Notification doesn't work in iOS with Firebase,

Trying to figure out why push notification doesn't work in iOS. Here is the code of push notification.It works fine in Android. Can you please help me ?

public function notification($token, $load, $type = NULL) { $url = 'https://fcm.googleapis.com/fcm/send';

            $fields = array(
                'registration_ids' => $token,
                'data' => $load
            );
            // 'notification' => $load
            $headers = array(
                'Authorization: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($ch, CURLOPT_SSL_VERIFYHOST, 0);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
            curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
            // echo json_encode($fields);
            $result = curl_exec($ch);
            echo curl_error($ch);
            if ($result === FALSE) {
                die('Curl failed: ' . curl_error($ch));
            }
            curl_close($ch);
            return $result;


        }