Every now and then, I get a ahead of myself. I’ve updated a typo in the script on the gallery, a vestige of when I updated the script to use server-side filtering. The bug revealed itself when you did not use the -Domain parameter.
Shout out to ITPro-Tips for letting me know! The updated version is here: https://gallery.technet.microsoft.com/Forwarding-Address-Import-5b3ead8e