"option src_ip" must have no space between the "!" and the IP address.
Since "option src_ip" is parsed as space separated list for "config rule" sections,
your "option src_ip '! 192.168.1.0/24'" is interpreted as list src_ip '!'
list src_ip '192.168.1.0/24' which leads to an error like Warning: Option @rule.src_ip has invalid value '!'
A workaround is to remove the space between the exclamation mark and the address.
The work around (removing the space) places the rule on my iptables!
It seems to hit all packets, but calls the thats WAN's drop chain. I see zero drops, which is expected (since I have a Custom RAW table rule dropping incoming from the LAN bridge also not equaling the SRC address).
I will test the space parsing in the next release.