[musictlk] Question about digital pianos

[Joshua Lester]

While I was at the convention in Dallas, a pastor friend asked me to
minister at his church.
When I went over there to practice, I noticed that he had a 2-stack keyboard.
He had a full sized digital piano, and on top of it, was a smaller keyboard.
My problem was that the sustaining pedal only worked on the top
keyboard, but wouldn't work on the piano.
Why was that?
How can he get the pedal to work on both keyboards?
Thanks, Joshua