Implement a custom notification system using Firebase, where each user is registered with a unique user ID on the Firebase Cloud Messaging server. Notifications are sent based on the average prediction of all account balances falling below the $25 threshold, rather than individual predictions.

Create a dedicated Pub/Sub topic for each user and deploy a Cloud Function that triggers a notification whenever the model predicts that a specific user's account balance will drop below the $25 threshold.

For each user, establish a Pub/Sub topic and deploy an application on the App Engine standard environment that sends a notification when the model predicts that the user's account balance will drop below the $25 threshold.

Leverage Firebase Cloud Messaging (FCM) by building a notification system where each user is registered with a unique user ID. Notifications are sent individually based on the model's prediction that a specific user's account balance will drop below the $25 threshold.

Combine the use of Firebase Cloud Messaging for notification delivery with Pub/Sub topics for each user to ensure scalability and real-time processing. Notifications are sent based on individual predictions.