LE have recently update their ToS again and Virtualmin has yet to release an update for this (as far as I can tell).
If you receive agreement notifications which are preventing you from obtaining or refreshing your LE SSL certificates, here’s what you need to do:
"agreement": "https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf",
Chris: Adelphia Interactive
Desktop: Windows 10 Pro x64
Server: Ubuntu 16.0.4.2LTS
Webmin/Virtualmin: Latest (daily updates)