I have the same issue - this shows up when trying to enable systems table and following the docs Monitor usage with system tables - Azure Databricks | Microsoft Learn

I'm getting exactly the same response on REST request to the UC API for a list of available schemas. When trying to ignore the status and making a PUT call to enable any of them, this (as expected) fails  
```

{"error_code":"INTERNAL_ERROR","message":"System schema \"billing\" is not currently available for enablement",

```