A SysOps administrator must set up notifications for whenever combined billing exceeds a certain threshold...

To set up notifications for when combined billing exceeds a certain threshold for all AWS accounts within an organization, follow these steps:

Enable Billing Alerts:

In the payer account, go to the Billing and Cost Management console.

Under "Billing preferences", enable the "Receive Billing Alerts" option.

Set Up a Billing Alarm in CloudWatch:

Navigate to the CloudWatch console.

Create a new billing alarm, specifying the threshold for the combined billing amount.

Set the alarm to publish a notification to an SNS topic when the threshold is breached.

Publish SNS Message:

Create an SNS topic to receive the billing alarm notifications.

Configure the billing alarm to send notifications to the SNS topic.

Setting Up a CloudWatch Billing Alarm

AWS Billing and Cost Management User Guide