Order Bump

Hey there!

I need to add an order bump to the final checkout process page (where the user enters payment info). (What is an order bump?)

Basically, a button that edits the invoice currently displayed to add/remove a product. I can find a method "acpAddToInvoice", but that's for the admin side. Is there a method to edit the invoice? Or should I perhaps just alter the database record of the invoice and reload the page?

Anyone encountered editing an invoice from the user side?

Ty!