Infracast PIN support was added in version 2.4.3 for AirServer Connect 4K UHD.

Unfortunately, this feature only works with devices running Windows 10 build 1809 or later. This is because Infracast PIN support was only added in build 1809 for Windows 10. When using Infracast (connected through infrastructure) all Windows 10 versions prior to build 1809 will connect to AirServer Connect 4K UHD without a PIN prompt even though PIN support is activated in the settings.