Foot pedal screen controls
When you add a foot pedal to a layout, by default the first foot pedal you add is configured to receive expression messages, and the second foot pedal you add is configured to receive volume messages.
By default, expression pedal screen controls pass through the MIDI messages for their common functions (expression or volume). If you want to use an expression pedal screen control to control another parameter, choose “Don’t pass thru” from the MIDI thru pop-up menu in the Screen Control Inspector.