We just upgraded to v5 from v4. emailed reminders are sending but have a URL that gives a 404.
the button on the email produces: https:/ourinvoice.domain.com/invoices/1402
It looks like the upgrade doesn’t fix $viewButton → $view_button. $viewButton doesn’t work and gives a 404 when clicking the generated button. $view_button produces a link that is usable.
Hope this helps someone else.