This is a tricky one, What does the totalUsers field look like in the UI? Without actually seeing all of your properties and having a play this is going to be a case of trying different values to see what works.
It seems there is no way to filter the event count I need from the node directly. I just want to get some custom event event count for the metric… even the official API doc, I cannot find any example at all… Wondering if it is even doable…