You can send accrual balances from the payroll system to WFH with the Update Accruals endpoint:
Note that the value sent as part of the Update Accruals endpoint will overwrite whatever value the accrual category currently has as of the date indicated. You cannot use the Update Accruals endpoint to adjust the accrual value by an incremental amount.
Please use the bulk aspect of this route, rather than calling it for each employee/accrual update, to reduce the number of api calls needed. Sending data on many employees without using the bulk aspect may cause throttling and impact the performance of your integration.