The input characteristics in the help found in C125 define the requirements for the dig input:
- Dig input.jpg (39.01 KiB) Viewed 4169 times
It doesn't do voltage detection, its a logic level switch.
The thresholds are outlined, and the switch needs to be wired to suit this. If the switch is set to active low the button should be wired between Dig and 0V and be of normally open operation. Then when the button is pressed, it will pull below the threshold and trigger.
You can also go to online > monitor channels and check if the button state is changing between 0 and 1 when you press it.