Is it something that can be fixed? More than likely. There are two places a coin must pass in order to play the machine. First the coin must match a sample coin in the coin comparitor. As long as the comparitor is functioning properly and the coin matches, it will be allowed to pass through. If not, this is where the coin will be rejected and returned to you. After passing through the comparitor, the coin falls through a chute and this is when the coin credits the machine. In the chute is an optic with a prism. These need to be cleaned periodically.
So you