Updates the invoice status of one or more billing schedule records, and recalculates the totals of their billing headers.

• Allowed change: only a record in Pending Billing can be updated, and only to Invoiced. The record's billing schedule details get the derived invoice status Invoiced as well.
• Per-record results: each record is validated on its own. A record that is not found or can't change status is returned with IsSuccess set to false and an ErrorMessage, and the other records are still updated.
• Status codes: 200 when every record is updated, 207 when only some are, and 400 when none are.
• Billing header totals: TotalInvoicedAmount, PendingInvoiceAmount, TotalAdjustedAmount and TotalBillIncludingAdjustments are recalculated for the billing header of every record found.