Invalid target type 'number', valid types: condition, token, topic, unknown using laravel 10

In my Laravel 10 application, I’m trying to send an OTP to a mobile phone using Firebase. I have integrated Firebase into my project and followed the relevant documentation for sending OTPs. However, when I try to send the OTP, I encounter the error message ‘Invalid target type ‘number’, valid types: condition, token, topic, unknown’. I have checked my code and made sure that I am using the correct target type. Could you please help me understand what might be causing this error and how I can successfully send the OTP using Firebase?

Error message:

"message": "Invalid target type 'phone_number', valid types: condition, token, topic, unknown",
    "exception": "Kreait\Firebase\Exception\InvalidArgumentException",
    "file": "C:\xampp\htdocs\daralaman-api\server\vendor\kreait\firebase-php\src\Firebase\Messaging\MessageTarget.php",
    "line": 58,
    "trace": [

otpRegistercontroller

`class OtpRegisterController extends Controller
{

    public function register(Request $request)
    {

        // Validate the request data
        $validator = Validator::make($request->all(), [
            'name' => 'required',
            'phone_number' => 'required|numeric',
        ]);

        if ($validator->fails()) {
            return response()->json(['errors' => $validator->errors()], 400);
        }

        // Generate a random OTP
        $otp = mt_rand(100000, 999999);

        // try {
        // Create a new user in the users table
        $user = User::create([
            'name' => $request->input('name'),
            'phone_no' => $request->input('phone_number'),
        ]);

        // Calculate the expiration time
        $expiresAt = Carbon::now()->addMinutes(2); // Expiration time set to 2 minutes from now 

        // Create a new OTP entry in the user_otps table
        UserOtp::create([
            'user_id' => $user->id,
            'otp' => $otp,
            'expires_at' => $expiresAt,
        ]);

        // Send the OTP to the user's mobile number using Firebase
        $factory = (new Factory)->withServiceAccount(storage_path('firebase/serviceAccountKey.json'));
        $messaging = $factory->createMessaging();

        $message = CloudMessage::withTarget('phone_number', $request->input('phone_number'))
            ->withNotification(Notification::create('OTP', "Your OTP is: $otp"))
            ->withData(['otp' => $otp]);

`
        $messaging->send($message);

        // Return a response indicating success
        return response()->json(['message' => 'OTP sent successfully']);
        // } catch (Exception $e) {
        //     // Return an error response
        //     return response()->json(['error' => 'Failed to register user'], 500);
        // }
    }

}