@Iwan Aucamp
Based on your description, it seems like you are encountering an authentication issue when trying to call the Unity Catalog API. It is possible that the AzureAD access token you are using does not have the necessary permissions to access the Metastores endpoint.
One potential solution could be to try using a Databricks personal access token (PAT) instead of an AzureAD access token. PATs are specifically designed for accessing Databricks APIs and may have the necessary permissions to access the Metastores endpoint.