You may wired the other switch wrongly. Please turn off the power at the circuit and check your wiring as the user guide illustrate.
Please check the LEDs. If all the LEDs are off:
• Make sure that you restore power to the wall switch at the circuit breaker.
• Make sure the wall switch is wired correctly.
• Make sure your primary switch has been installed in electrical box with both live and neutral wire. If you are not sure, switch installation position of your primary and add-on switch and try again.