Thank you so much @pedro_rocha
It worked fine.
Both APIs /grid/account/{id}/usage from grids' API perspective and /storage/aggregates?fields=space.cloud_storage.used from clusters' API perspective are showing same numbers (used space is same)
However on the GRID GUI console, used space is close to 2X more than what I am seeing from APIs.
Not sure why this difference is there, Any thoughts. Thanks.