I think your mm param is mis-formed. According to the spec, you can only combine multiple conditional params. Yet, your first param (2) is not conditional. Can you rewrite the whole expression as a set of conditional parameters and see if this goes away.
Or, I would try from their example (2<-25% 9<-3) and see if you get the same issue. If you do not, keep modifying it towards yours until you hit the problem or get what you need.