Azure Policy does not support tagging subscriptions directly, including at creation time. It only works for resources and resource groups.
You can use an Azure Automation Account with a scheduled PowerShell Runbook that:
Lists subscriptions under a management group (e.g., "Prod").
Checks for required tags and adds only missing ones.
Uses Set-AzTag -Operation Merge to preserve existing tags
I hope this information is helpful. Please feel free to reach out if you have any further questions.
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