You can only use a single switch per expression pedal port, and it has to be wired specially:
Tp to 10 k resistor
Ring to other side of 10k resistor AND to one side of switch
Sleeve to other side fo switch
It will send the maximum CC when the button is released, and the minimum CC when the button is pressed.
You can also use position switch actions to do more than CCs. I recommend setting the switch position using an expression pedal set about half way in it's travel, then you can start using the pushbutton.