A client confirmation is a workflow step that pauses the workflow until the client explicitly confirms something. It could be anything: that all transactions up to a certain date have been recorded, that they're happy for you to file, or that the information they've provided is complete and accurate.
The client receives an email with a link. They click it, see a branded confirmation page with your message, and click a button to confirm. That's it — the step completes and the workflow moves on.
No portal login required. No back-and-forth emails. One click from the client and the workflow continues.