If your customers have committed usage billing, you can set up automatic email notifications to alert them when they're approaching their pre-committed usage limit.
To enable usage-based notifications:
Head to Customers > All subscriptions.
Select the subscription you'd like to enable usage threshold notifications for.
Scroll down to the Usage section and click the
bell icon for a product with committed usage. Only products with committed usage are eligible for usage notifications.
Enable Notify me by email when my usage exceeds a certain threshold.
Enter the percentage threshold.
Add CC and/or BCC emails if you'd like the notification to be sent to someone other than the billing email on file for the customer, which is added by default.
Save changes.