Currently you cannot update an Invoices DueDate or PlannedPaymentDate via the API if there are payments or credit notes allocated to it. This is problematic especially for invoices (such as business rates) that get paid in (monthly) installments.

If the DueDate or PlannedPaymentDate has passed then these invoices do not show up in the Short-term CashFlow view.

I can update the Planned Payment Date through the UI (and I can update the DueDate through the UI as well) regardless of if the invoice has a credit or payment against it, so why doesn't the API provide the same validation as the UI?