Support multi-project invoices via the public API (invoice[project_ids][])

Hi all,

I’d like to request that the public REST API be extended so a single invoice can pull timeslips from multiple projects, matching the behaviour already available in the FreeAgent web UI.

Use case:

I occasionally bill a single client across more than one project in a single monthly invoice. In the web UI this is straightforward: When creating an invoice for a contact, I can pick a primary project and add additional projects, and the resulting invoice includes timeslips from all of them, grouped by task.

When I create a multi-project invoice in the FreeAgent web UI, the browser submits a form to the in-app endpoint with this shape (relevant fields only):

 invoice[contact_id]=<contact-id>                                                                                                                                                                                           
 invoice[project_id]=<primary-project-id>                                                                                                                                                                                   
 invoice[project_ids][]=<additional-project-id>
 invoice[project_ids][]=<another-additional-project-id>                                                                                                                                                                     
 invoice[include_timeslips]=billed_grouped_by_timeslip_task              

So the underlying data model clearly already supports an invoice referencing multiple projects.

I would love to do the same thing programmatically, but I can’t find any support for this in the public API.

Would it be possible to support this? Clearly it would need to be backwards compatible so that single-project invoices are unaffected.

Happy to test any beta/preview if helpful.

Thanks!