In my experience its one of those solved problems where only a handful of products do it well, and well = pretty terrible for anyone SMB.
It's not hard, but everyone who can do it well has noticed what their competition is charging and followed suit.
It was a complicated software package that did nothing out of the box and everything required significant configuration of the rule engine to account for the customer’s needs. It shipped with some building blocks for the rule engine but often/always required custom code to facilitate things the customer needed.
My job was to fly out to customer sites and perform the custom implementation tasks.
We now use a pen and paper. I've looked at open source options, the landscape is not great.