Update model-fido2.md

docs/model-fido2.md

@@ -1,6 +1,6 @@
 ## How is UV handled in mailcow?
 
-The UV flag (as in "user verification") enforces WebAuthn to verify the user before it allows access to the key (think of a PIN). We don't enforce but prefer UV to allow logins via iOS and NFC (YubiKey).
+The UV flag (as in "user verification") enforces WebAuthn to verify the user before it allows access to the key (think of a PIN). We don't enforce but prefer UV to allow logins via iOS and NFC (YubiKey). W
 
 ## Login and key processing
 
@@ -13,3 +13,11 @@ When calling the login process, the authenticator is not given any credential ID
 ## Who can use WebAuthn to login to mailcow?
 
 As of today, only administrators and domain administrators are able to setup WebAuthn/FIDO2.
+
+## iOS problems
+
+Please use a desktop computer to register your key with your mailcow account.
+
+The process was tested using a YubiKey with Chrome on Windows. When registering a new, empty key, you will be prompted for a PIN for the new YubiKey. Once set and confirmed, the credentials are stored on the key. Using it with iOS works flawless now.
+
+iOS seems not to be able to set a PIN on the device on first use, so please use a desktop computer for this step.