Adjust the default payment plan of an Invoice

I’m creating invoices via the XML-RPC API, and when doing so a payment plan is automatically created with a due date set to the date created. I’d like to instead set the due date to some date in the future (the invoice is not immediately due but the due date is shown within fortapay).

I’ve already set the Order Date to the future date which should be the Due Date, but the Due Date is still being set to today by default.

I can’t find any API methods for modifying a PayPlan (other than to apply a manual payment). I’ve tried modifying the PayPlan via the DataService API but the table is Read-only.

I don’t actually want a multi-payment payment plan - I just want a single payment with a specified date in the future. How do I accomplish this via the API?

A colleague suggests the following…

Create a new Payment Plan through the UI. Then, in OrderService.placeOrder, set planID to the Payment Plan. (Each Plan’s id is shown in the URL. I don’t think it’s displayed anywhere on-page.)

Thanks - but I don’t think that’ll help. Payment plans created in the UI don’t have a “Due Date”, only a “Days Until Start”. I need to create different due date for each order I’m generating through the API. I really don’t need a “payment plan”, but one is created automatically and specifies a due date that’s not correct.