You haven’t really given us much to go on here. It could be any one of many different issues. Give us a bit of background and let us know what you’ve tried and maybe we can help.
The iPad Air 2 is an older tablet, so is this a tablet that you’ve had for a while or did you just get it? If you just got it was it used or new? If you’ve had it for a while did Touch ID ever work reliably or has it always been a problem? Have you tried reregistering your finger or registering a different finger to see if that makes a difference?