Send Firebase Notification to more than 1000 users at a time from PHP

send_firebase_notification.php

<?php 
    /** 
	 *  Created By : Pratik Butani
	 *  Created Date : 24/10/2018
	 */
    // Database Connection
    include "conn.php";

	// Get Records from Table
	$sql = "SELECT * from fcm";
	
    // Check Results
	$result = mysqli_query($conn, $sql);
	
	if (mysqli_num_rows($result) > 0) {
		
		// output data of each row in Array
		$array = [];
		while($row = mysqli_fetch_assoc($result)) {
			$array[] = $row["fcm_token"];
		}
		
		// Chunk of Array with 999 Records, I have not taken risk for 1000 users :D
		$final_array = array_chunk($array, 999);
		
		// Loop for Every Sub Array and Send to FCM Server
		foreach($final_array as $array_of_chunk) {

    		#API access key from Google API's Console
			# Kindly Replace it with Your API key and Token
    		define( 'API_ACCESS_KEY', 'AIzaSyCY6U_vT_bA-J__RuOApClcm7VbFWYuadfa');
    		$registrationIds = $array_of_chunk;
    
    		#prep the bundle
    		 $msg = array
    			  (
    			    'title' => mysqli_real_escape_string($conn, $_POST['title']),
    				'description' => mysqli_real_escape_string($conn, $_POST['description']),
    				'url' => mysqli_real_escape_string($conn, $_POST['url']),
    				'admin' => mysqli_real_escape_string($conn, $_POST['admin'])
    			  );
    			  
    		$fields = array(
    					'registration_ids' => $registrationIds,
    					'data' => $msg,
    			      );
    			
    		$headers = array
    				(
    					'Authorization: key='.API_ACCESS_KEY,
    					'Content-Type: application/json'
    				);
    				
		    #Send Reponse To FireBase Server	
			$ch = curl_init();
			curl_setopt( $ch,CURLOPT_URL, 'https://fcm.googleapis.com/fcm/send' );
			curl_setopt( $ch,CURLOPT_POST, true );
			curl_setopt( $ch,CURLOPT_HTTPHEADER, $headers );
			curl_setopt( $ch,CURLOPT_RETURNTRANSFER, true );
			curl_setopt( $ch,CURLOPT_SSL_VERIFYPEER, false );
			curl_setopt( $ch,CURLOPT_POSTFIELDS, json_encode( $fields ) );
			$result = curl_exec($ch );
			curl_close( $ch );
		}
		
		$result_final = array("result" => true, "message" => "Data Fetch Successfully.");
		
		echo $result_final;
	
	} else {
		$result_final = array("result" => false, "message" => "Error in Fetching Data.");
		echo json_encode($result_final);
	}
?>

not working