FC-3 expression jack not seeing hardware

Just bought an FC-3 and whilst it's easy to set the three foot switches up, I cannot get anything from the jack socket for expression pedal.

I'm trying to connect a momentary foot switch to have my stage partner be able to advance to the next setlist item in Studio One Show Page. I have already mapped 1 & 3 buttons to next/previous, and the 2 button to tap tempo, all good and simple. But when I connect the foot switch the expression jack and try to set up CC command, the editor tool tells me "wrong type of pedal" I've tried with a sustain pedal also but get the same result. Any ideas please?