An order may be marked as In Transit because the invoice was not finished. Please ensure that during servicing your drivers are capturing a signature or indicating that a signature was not captured. They can then hit the Finish Invoice button in the Stock app.
Parlevel Hero Support can modify a route status to "With Pending Services" so that a signature can be added through Stock and the invoice finished from there. This will mark it as Delivered, at which time the invoice will show up under OCS > Invoices.