Not familiar with those brakes but apparently the magnetic button is part of the brake, not the pad.
From a review:"A little tricky to install because of the tiny little circular magnets that are in the actuator assembly. These magnets tend to stick to the brake pad's metal backing and are difficult to put back where they belong. It would be nice to know where to get replacement magnets because they are very easy to lose if dropped on a garage floor!". I suspect your other magnet is either still inside or has been lost.