deconz-rest-plugin: Connect to Rest API problem

Hi, I am having trouble to connect to REST API via https://dresden-elektronik.github.io/deconz-rest-doc/getting_started/

I launch the GET command and receive: [ { "id": "00212EFFFF04FF93", "internalipaddress": "172.30.33.0", "macaddress": "00212EFFFF04FF93", "internalport": 40850, "name": "Aqara Gateway", "publicipaddress": "31.17.161.51" } ] So the next step would be to connect APP/Gateway - which I released in the DeConz frontend. Within the 60 sec I launched the POST command (or whatever this is called):

172.30.33.0:40850/api incl. the text { "devicetype": "my application" }

I am receiving the message

Could not get any response .This seems to be like an error connecting to

http://172.30.33.0:40850/api. The response status was 0.

Check out the W3C XMLHttpRequest Level 2 spec for more details about when this

happens.

Do I have to forward any port ( I tried via Fritzbox, but the IP address is not in a valid subnet of my Fritzbox…) ?

Best regards, Jörg