Cant connect new Icinga for Windows to director

Hi there,
as we had some issues with the Icinga2 windows agent I was really happy when Icinga for Windows 1.0 was announced. I tried it out to set it up using the kickstart script and I have some issues to connect it to our director.

I always (no matter on which of the three agents I tried) the error of

Starting Icinga Agent installation wizard
=======
Do you want to use the Icinga Director Self-Service API? (Y/n):
Please specify the Url pointing to your Icinga Director: https://FQDN.my.domain.de/director/
Do you want to manually override arguments provided by the Director API? (y/N):
Please enter your Self-Service API key: MYVERYLONGAPITICKETFROMDIRECTOR
Failed to connect to your Icinga Director at "https://FQDN.my.domain.de/director/". Please try 
again
Please re-enter your SelfService API Key for the Host-Template in case the key is no longer 
assigned to your host (Default: "MYVERYLONGAPITICKETFROMDIRECTOR"):

I am pretty sure that the server URL works…at least this is the URL on which I can access the installation and all pages of director can be found (yes, icinga is installed as root web application).
Everything is working fine when configuring everyting manually.

Honestly I think the documentation of the new Icinga for Windows is a little bit too short, especially on those installation / configuration parts.

Anybody any ideas?

Best & Thanks,
M.