.NET Firebase Send Push Notification Error

Sending messages through FCM was working yesterday, but today I'm getting this error:

Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.

As a first step, I created a new JSON file in Firebase, but I'm still getting the same error. How can I fix this?

public async Task SendPushNotificationAsync(string fcmToken, string title, string message)
{
    if (string.IsNullOrWhiteSpace(fcmToken))
    {
        _logger.LogWarning("FCM token is null or empty");
        throw new ArgumentException("FCM token cannot be null or empty", nameof(fcmToken));
    }

    if (FirebaseApp.DefaultInstance == null)
    {
        _logger.LogError("Firebase App is not initialized. DefaultInstance is null");
        throw new ApplicationException("Firebase App is not initialized");
    }

    var notification = new Message
        {
            Token = fcmToken,
            Notification = new FirebaseAdmin.Messaging.Notification
            {
                Title = title,
                Body = message
            },
            Apns = new ApnsConfig()
            {
                Aps = new Aps()
                {
                    Alert = new ApsAlert()
                    {
                        Title = title,
                        Body = message
                    },
                    Sound = "default",
                    Badge = 1,
                },
            }
        };

    try
    {
        _logger.LogInformation("Sending push notification to token: {Token}", fcmToken);
        var messageId = await FirebaseMessaging.DefaultInstance.SendAsync(notification); // Error Line 
        _logger.LogInformation("Push notification sent successfully. Message ID: {MessageId}", messageId);
    }
    catch (Exception e)
    {
        _logger.LogError(e, "Error sending push notification to token {Token}", fcmToken);
        throw new ApplicationException($"Error sending push notification: {e.Message}", e);
    }
}

Service CTOR:

public FirebasePushService(IConfiguration configuration, ILogger<FirebasePushService> logger, IWebHostEnvironment environment)
{
    _logger = logger;

    // Initialize Firebase Admin SDK if not already initialized
    if (FirebaseApp.DefaultInstance == null)
    {
        var firebaseConfigPath = configuration["Firebase:ConfigPath"];

        if (string.IsNullOrEmpty(firebaseConfigPath))
        {
            throw new ApplicationException("Firebase:ConfigPath configuration is missing");
        }

        // Try to find the file in multiple locations, using ContentRootPath as primary source
        var possiblePaths = new[]
            {
                firebaseConfigPath,
                Path.Combine(environment.ContentRootPath, firebaseConfigPath),
                Path.Combine(AppDomain.CurrentDomain.BaseDirectory, firebaseConfigPath),
                Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "..", firebaseConfigPath)
            };

        var configPath = possiblePaths.FirstOrDefault(File.Exists);

        if (configPath == null)
        {
            _logger.LogError("Firebase configuration file not found in any of these locations: {Paths}", 
            string.Join(", ", possiblePaths));
            throw new ApplicationException(
                    $"Firebase configuration file not found in any of these locations: {string.Join(", ", possiblePaths)}");
        }

        try
        {
            _logger.LogInformation("Initializing Firebase with config file: {ConfigPath}", configPath);
            FirebaseApp.Create(new AppOptions()
                {
                    Credential = GoogleCredential.FromFile(configPath)
                });
            _logger.LogInformation("Firebase initialized successfully");
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to initialize Firebase Admin SDK");
            throw;
        }
    }
}