Trouble with iphone Vcam with Gamepad controlling focal length

Hoping someone can help me out. I’ve got my iPhone set up with a controller, I’d like to use the buttons as somewhat controls for my vcam. I have the face buttons mapped out great, but I can’t for the life of me figure out how to adjust the focal length with the triggers. I’ve been lost in an enhanced-input black hole, and just feel there’s no way something this simple is this complicated. When I remap my vcam inputs and set to focallenth or focal length axis I get nothing. I’ve played around extensively with modifiers, changed input in the input mapping blueprint, the event graph for the focal length modifier itself, as well as the project settings… nothing.

How can I set this up so my iPhone vcam can easily zoom in and out?