How to enable TouchID

With the latest version it is possible to enable touch ID for additional protection - thanks for this feature!
However, this setting in the security settings is disabled on my iPad and iPhone. Any ideas?

Which iPad/iPhone and which iOS version do you use?

Have you set up a passcode in the security settings? You need to first set up a passcode before you can enable touch or face ID.

iOS 11.2.6

Thanks for the hint, now it works!