Finger print

If Touch ID isn't working on your iPad, read this support article --> If Touch ID isn't working on your iPhone or iPad - Apple Support

"Follow these steps. Try using Touch ID after each step: Make sure that you have the latest version of iOS. Make sure that your fingers and the Home button are clean and dry.* For the Home button, use a clean, lint-free cloth to wipe off any dirt or debris. Your finger should cover the Home button completely, touching the surrounding metal ring. While Touch ID is scanning, you shouldn't tap too quickly or move your finger around. If you're using a case or screen protector, make sure it doesn't"