pfSense

• in DHCP server config, MAC Deny option is set with a MAC address
• user wants to not log that every few seconds so checks option "Ignore denied clients"
• DHCP Server fails to start with an error:

Error: /etc/dhcpd.conf line 22: expecting a parameter or declaration

line 22:
ignore members of "c81f664xxxxx";

Unchecking that option changes it to:
deny members of "c81f664xxxxx";
...which lets the DHCP service start.

Removing the entry from MAC Deny and checking the box lets the service start.

Possibly a solution would be to set the two lines to be:

deny members of "c81f664xxxxx";
ignore unknown-clients;

instead of:
ignore members of "c81f664xxxxx";
ignore unknown-clients;

..but didn't test that since the file /var/dhcpd/etc/dhcpd.conf is overwritten when the service starts.

Forum thread: https://forum.netgate.com/topic/165267/dhcp-restriction-problem

I tried this on 22.01 on a 3100. The thread is from July 2021 so is presumably an earlier version.