If your amp is not a MIDI controlled amp, and only has a footswitch jack for switching channels, it's likely that the BRIDGE controller is not able to be used. We created the CLiCK Relay Switcher specifically for this purpose.
The Flexiport mode "Switch Out" which is used to emulate an analog switch has a voltage limit of 3.3v. Most Amp, and certainly older ones will pass a much higher voltage through the Aux Footswitch jack.
Before using the Switch Out Flexiport mode, we recommend checking the voltage of the target device's jack with a multimeter to make sure the voltage is not above 3.3v.