After changing the configuration of a firewall the journal may report an error when restarting the firewall service such as the following:
ERROR: ‘/usr/sbin/iptables-restore -w -n’ failed: iptables-restore v1.8.2 (nf_tables):
This issue seems to be caused by a Debian bug documented here.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914694
The workaround is to change the valued of IndividualCalls to yes in /etc/firewalld/firewall.conf
IndividualCalls=yes