push.php

<?php
public function sendMessage($data, $token, $notificationType)
    {
        $url = 'https://fcm.googleapis.com/fcm/send';
        /**
           * * If you'd like to send to mulitple devices 'registration_ids' => [$tokens],
         */

        $postFields = json_encode([
            'to' => $token,
            'data' => ['message' => $message]
        ]);

        $headers = [
            'Authorization: key=' . $this->gcmKey,
            'Content-Type: application/json'
        ];

        $ch = curl_init();

        curl_setopt_array($ch, [
            CURLOPT_URL => $url,
            CURLOPT_POST => true,
            CURLOPT_HTTPHEADER => $headers,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_POSTFIELDS => $postFields,
            CURLOPT_TIMEOUT => 30,
        ]);

        $result = curl_exec($ch);

        if ($result === false) {
            throw new \Exception('Curl failed: ' . curl_error($http2ch));
        }

        $status = curl_getinfo($ch, CURLINFO_HTTP_CODE);

        $jsonResult = json_decode($result);

        $reason = null;

        if (isset($jsonResult->results[0]->error)) {
            $reason = $jsonResult->results[0]->error;
        } else {
            $reason = 'All Good';
        }