Use the CloudFormation detect root cause capability for the failed stack to analyze the failure and return the event that is the most likely cause for the failure.

Query failed stacks by specifying the root stack as the ParentId property. Examine the StackStatusReason property for all returned stacks to determine the reason the nested stack failed to deploy.

Activate AWS Systems Manager for the AWS account where the application runs. Use the AWS Systems Manager Automation AWSSupport-TroubleshootCFNCustomResource runbook to determine the reason the nested stack failed to deploy.

Configure the CloudFormation template to publish logs to Amazon CloudWatch. View the CloudFormation logs for the failed stack in the CloudWatch console to determine the reason the nested stack failed to deploy.