{"multicast_id":8972998920482382311,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"InvalidRegistration"}]} : i want to send push notification from web to android devices but it responses invallid registration


i tried to send from firebase consol but is does not include message data 

<?php 

//$con= new mysqli("localhost","root","","doctor_appointment");
include('connection.php');

	$sql = " Select * From token_register where id = 1";

	$result = mysqli_query($connection_to_db,$sql);
	$tokens = array();

	if(mysqli_num_rows($result) > 0 ){

		while ($row = mysqli_fetch_assoc($result)) {
			$tokens[] = $row["token"];
			// $token = $row["token"];
			// echo "$token";
		}
	}

	mysqli_close($connection_to_db);

	


	function send_notification ($tokens, $message)
	{
		// define( 'API_ACCESS_KEY', 'AIzaSyDt2xaRw4XGzghfxAMRFVy-I8ZeacBDbHA');
		$url = 'https://fcm.googleapis.com/fcm/send';

		$fields = array(
             'registration_ids'  => array($tokens),
             'data'              => array( "message" => $message ),
             );

		$headers = array(
			'Authorization:key = AIzaSyDdHTdvqzN8lrUqhZKOeuiR2d9cETRBhNw',
			'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));
       $result = curl_exec($ch);           
       if ($result === FALSE) {
           die('Curl failed: ' . curl_error($ch));
       }
       curl_close($ch);
       return $result;
	}
	$message = array("message" => " FCM PUSH NOTIFICATION TEST MESSAGE");
	$message_status = send_notification($tokens, $message);
	echo $message_status;
	

	



 ?>


i expected to be {"multicast_id":7068539387015084016,"success":1,"failure":0,"results":[{"RegistrationSuccess"}]}  but responses {"multicast_id":7068539387015084016,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"InvalidRegistration"}]}