ipad air will not accept my finger print to unlock

From time to time the iPad will ask you to enter your passcode to re-enable the finger print reader. Once you see this, just enter your passcode and the next time you log in it should work again until it needs the passcode again. You should remember the passcode that you have given your iPad as it IS going to ask for this from time to time. Just enter your passcode and it will open your iPad. If it is now disabled then you’ll need to follow the instructions here If you forgot your iPad passcode - Apple Support

iPadOS required entry of the passcode at least weekly.

If you don’t know the passcode, your only option is to completely reset (erase) the device and start-over from an available backup.

If you see an iPhone or iPad unavailable message or Security Lockout screen – Apple Support (AU)