BFS-U3-200S6M External Trigger

We are attempting to trigger our FLIR BFS-U3-200S6M camera using an Adafruit Metro board. We are following the BlackflyS directions listed here:

But instead of triggering one camera with another we use the arduino as the camera clock.
Confusingly when line3 is configured as an input we see 3V and does not respond to logic level from arduino.

Does anybody have any experience working with these FLIR cameras in a similar context.