Suction cups fail to stick to windscreens when the screen is not absolutely clean
For best results; clean the glass with an alcohol based cleaner to ensure maximum suction with the mount.
Some glass cleaners can leave a residue that interferes with the suction.
Smoking in the car can also leave a residue on the glass that will affect the suction
Alcohol pre-injection swabs are recommended and are available at your local pharmacy.
If your car's windscreen is curved, you may have a better result attaching your suction cup to a flatter part of the screen.
SAFETY NOTE: Ensure that the location you choose for your camera does not affect the drivers vision of the road ahead.