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Check to make sure in the Alias field called your Path expression field has the following:  cidr

Under Step 1 of the instructions link I posted.  Does your Alias match exactly what they documented, if you are missing anything, it wont work.

Gotta add "Path Expression"  CIDR  found here:  https://docs.opnsense.org/manual/how-tos/drop.html

As long as the rule is working, I block in and out of my wall, try port 80 browsing to: http://(breaking on purpose)45.148.123.12
looking at your live firewall log, filter on "block" traffic should be there.