thanks @NandiniN , 

we have looked through that documentation and still have not been able to get anything to work without the user also being an account or workspace admin.  The way i'm interpreting the documentation (screenshot) is the API currently only supports assigning a user a role (i.e. the Group Manager), but does not allow for adding or removing users from the group. When trying to patch we get error messages like "Members attribute cannot be updated as group newgroup can only be managed in account."

Hoping to hear if/when Databricks plans to support this?