40 Compute Units.
Reference: Here
Parameters
ledger_hash(string, optional) The unique hash of the ledger version to use.ledger_index(number or string, optional) The ledger index of the ledger to use, or a shortcut string such asvalidated.
Returns
type(string) The stringbookChanges.ledger_hash(string) The identifying hash of the ledger version used.ledger_index(number) The ledger index of the ledger version used.ledger_time(number) The official close time of the ledger, in seconds since the Ripple Epoch.validated(boolean) Iftrue, the information comes from a validated ledger version.changes(array) One book update object per order book that was updated in this ledger, each withcurrency_a(XRP_dropsfor XRP, otherwiseissuer/currency),currency_b,volume_a,volume_b,high,low,openandclose. Empty if no order books were updated.
{"id":1,"command":"book_changes","ledger_index":"validated"} to wss://mainnet.xrpl.validationcloud.io/v1/<YOUR_API_KEY_HERE>.