Side-chain gate not working

I’m following the manual (pg167) and I can’t get a gate to side-chain.

I’ve got a keyboard sound I want controlled by percussion.

Insert gate on the keyboard channel, activate the side chain button.

Open the send inspector on the percussion, select the gate on the keyboard channel.

And then, no sound comes from the keyboard channel. Threshold set from “0” to “-60”, nothing on the output. Visually the input of the gate is working, but nothing in the output. What am I doing wrong?