Some features require you to press the Home button two or three times in quick succession. Some users may find that they can’t press the button quickly enough to get a response. Fortunately, you can change the speed at which the device will register your presses.
Open Settings, General, Accessibility, then Home Button. Under the Click Speed section, choose either Slow or Slowest to change the speed needed. The selected option will flash to indicate the required pressing speed.