From iOS 16.4
To set up passkey on Apple devices, it is important that you have activated passkey. To use passkeys for iPhone and iPads, the iCloud keychain and two-factor authentication must be activated. You can find information on setting up passkey for iOS here: https://support.apple.com/de-de/guide/iphone/iphf538ea8d0/ios
Once passkeys are set up and enabled in iCloud Keychain, you can set up passkeys under Kaia back pain. After logging in with your email and password, the wizard for setting up passkey should start. In case of an error message when logging in, please exit the Kaia app or restart your mobile phone once.
From iOS18:
Please use the ‘Passwords’ app from Apple to be able to save your passkey. You can easily download it from the App Store. You can also use alternative apps from other providers, but the ‘Passwords’ app is linked to your Icloud keychain