@David-TP Update ! I managed to add port forwarding rules now. As you could see from my former reaction, I suspected it had something to do with the address reservation. I finally did find the...

@David-TP Hi David, Thanks for your reply. The current APP version I use (on Android) is 3.2.5 (The latest version available according to Google Play). I also tried it on an iPad with the latest iPad...

I Have now three port forwarding rules to my NAS, when I want to add a 4th rule it says it is not possible because the IP adress (of the NAS) is already in use.