Hi Jan,
thank you for your support.
The AAGUID to be entered in Azure and for YubiKey communicated is like described here:
The error message is:
The input must be in a valid Guid format. Example: 12345678-0000-0000-0000-123456780000
The Nitrokey is 4-CHAR longer than these other AAGUIDs (here: A0 FF).
It should be a 128-bit identifier.
Thanks