Dynamic text - SUM Length of filtered line features

[LISWaukesha_Co]

Trying to build a trail navigator and I'd like the user to see how many miles their hike will be.  I have two filters, one to pick the park they're in and one to pick which colored loop or loops they want to hike.  Filters seem to work great.  However...

I've tried to use the SUM({Shape.STLength()}) expression (also was going to convert to miles, but heck, I'd be happy with any result) to achieve this in the Dynamic Text and it doesn't want to work.  I tried just displaying the first random attribute and it seems to be reading the data OK, but when I try to switch to the expression I want to use, it just displays "Expression 2" no matter what I do.  Any ideas?

[jcarlson]

Experience Builder has very limited access to expressions of any kind. If you don't have the length stored as an attribute in the table, you probably won't be able to do this.

That said, you could calculate a new "miles" field for your trails layer, then display the sum of that.

[LISWaukesha_Co]

I've considered that, that perhaps the system length field isn't very compatible. I might try that, thank you for pushing me further down that path.