InvalidRegistration error in Firebase Cloud Messaging for Android

Question

I am developing an Android app that using Push Notification feature. I need to push from server. I use Firebase for it. This is my first time using Firebase. But when I push from server using PHP and CURL, it is giving me invalid registration error.

I get the Firebase token in Android like this

String token = FirebaseInstanceId.getInstance().getToken();

Then I save sent that token to server and saved in the database.

At server, I am pushing like this

class Pusher extends REST_Controller {

    function __construct()
    {
        parent::__construct();
    }

    public function notification_get()
    {
        $rows = $this->db->get('device_registration')->result();
        $tokens= array();
        if(count($rows)>0)
        {
            foreach($rows as $row)
            {
                $tokens[] = $row->token;
            }
        }
        $message = array("message"=>"FCM PUSH NOTIFICATION TESTING");
        if(count($tokens)>0)
        {
            $result = $this->send_notification($tokens,$message);
            if(!$result)
            {
                die("Unable to send");
            }
            else{
                $this->response($result, REST_Controller::HTTP_OK);
            }
        }
        
    }

    function send_notification($tokens,$message)
    {
        $url = 'https://fcm.googleapis.com/fcm/send';
        $fields = array(
                'registration_ids'=>$tokens,
                'data'=>$message
            );

        $headers = array(
                'Authorization:key = AIzaSyApyfgXsNQ3dFTGWR6ns_9pttr694VDe5M',//Server key from firebase
                '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($result==FALSE)
        {
            return FALSE;
        }
        curl_close($ch);
        return $result;
    }
}

I am using CodeIgniter 3 framework for building Rest API. When I push accessing URL from browser, it returns JSON data with error as in the below screenshot.

As you can see it is giving InvalidRegistration error and message is not pushed to devices. What is wrong with my code?

Additional

This is my FirebaseMessagingService class that show notification in Android

public class FirebaseMessagingService extends com.google.firebase.messaging.FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);
        showNotification(remoteMessage.getData().get("message"));
    }

    private void showNotification(String message)
    {
        Intent i = new Intent(this,MainActivity.class);
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        PendingIntent pendingIntent = PendingIntent.getActivity(this,0,i,PendingIntent.FLAG_UPDATE_CURRENT);

        NotificationCompat.Builder builder = new NotificationCompat.Builder(this).setAutoCancel(true)
                .setContentTitle("FCM Test")
                .setContentText(message)
                .setSmallIcon(R.drawable.info)
                .setContentIntent(pendingIntent);

        NotificationManager manager = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
        manager.notify(0,builder.build());
    }
}

Answer 1

Although I am not using codeigniter, I was encountering the InvalidRegistration error while sending to an iOS device, so I thought I would share my solution here.

I had to change registration_ids to to in PHP when sending a Notification message to a single device token, and make sure the value of to was a string and not an array.

Change this:

'registration_ids'=>$tokens,

To this:

'to'=>$tokens[0],