The authentication can fail if the maximum number of authentication attempts have reached or if the user is tapping any of the two prompt options. This would result into a descriptive error which your mobile app has to handle.
Want to explore more? You can download the sample code file “KeychainTouchID: Using Touch ID with Keychain and LocalAuthentication”. It’s available in the Apple developer library.
Below is the video where you can know more about Touch ID by Chris Gibbs:
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