A test authorization for monitor.packetfilters.net to the Let's Encrypt staging service has revealed issues that may prevent any certificate for this domain being issued.
Fetching http://monitor.packetfilters.net/.well-known/acme-challenge/IP2OHPWoal8TWPVBjKwRyTmG6sBcHIYx6SxwAKg_RKk: Timeout during connect (likely firewall problem)