I used a door bell, and put a piece of bracket right on top of the coin mech, so when you pull down the coin return lever it pushes the door bell button, and allows a vend.
you shouldn't use a doorbell push button, it isn't rated for line voltage ( it's only intended for low voltage use, ( in the U.S. low voltage is considered to be 75 volts or less) use a momentary/nomally open push button rated for line voltage 120/volts A.C. @ 1 amp minimum.