Before deploying Stable's CloudFormation stacks, you must enable the AWS StackSets feature in your AWS environment. Here's how to enable it:
Sign in to the AWS Management Console as an administrator
Navigate to CloudFormation in the AWS console
From the left navigation pane, select StackSets
If you haven't used StackSets before, you'll be prompted to enable it
Choose Self-managed permissions
CloudFormation will create the necessary IAM roles:
AWSCloudFormationStackSetAdministrationRoleAWSCloudFormationStackSetExecutionRole
Click Enable StackSets