I'm not familiar with Fritzbox routers and my German is out of practice, but that page looks like it is for port-mapping. Did you put the device in a "DMZ" on the router? If yes, you will probably need to access via the WAN IP address not LAN.
ok damn. That was it probably. Somehow I have to use 192.168.0.28 instead of 192.168.188.32. Don’t know why but thank you very much !