You should always ensure that your iPadOS or iOS version is the most recent. You should ensure that your Touch ID sensor and fingers are dry and clean. Go to Settings > TouchID & Passcode. Make sure iPhone Unlock or iTunes & App Store are on and you have enrolled at least one fingerprint. You can enroll a different finger.
If your hands are wet, oily, dirty, or moist, the fingerprint sensor might not work. If your fingerprint sensor is not working, your phone might not unlock. Wash your hands and dry it. Next, use the fingerprint to unlock your phone. office.com/setup
