I looked at the manual for this controller and sadly there is not 1 note about how to connect an E-Stop button. This is a major oversight IMO. Regardless, I have usually seen PIN 10 Used for E-stop. Not sure why but it seems to be a standard. Can you try swapping things around and put your button on 10 and configure as such?
HTH,
Sid
P.S. Active Low is OK/Normal