Help connecting external sustain pedal with PX 765

[PianoBeginner]

 

Purchased 'Donner Piano Sustain Pedal with Polarity Switch DK-1' and connected it to Casio PX765 piano's phones OUT. Piano sound stopped(as expected with headphones) and the pedal function didn't work. Tried switching the polarity switch too. Am I connecting it wrong? Am i supposed to connect it to the regular pedal box with some kind of adapter instead? Please help.

[Brad Saucier]

Sustain pedals are not compatible with headphone jacks.  External pedals are not compatible with this model piano.  The PX-765 comes with a 3 pedal unit that should be used for pedal operations. 

[PianoBeginner]

Thank you for clarifying that. I was going crazy searching for places to connect the sustain pedal.