TCP Outgoing Connection w. Docker-NodeRed

Question

first of all, I have to mention that I am a complete rookie in Docker and NodeRed :) I have a KNX visualization server running and want to establish a TCP connection with NodeRed. My NodeRed is running in a docker container on my Synology.

My flow looks like this:

The flow is waiting for an incoming "Hallo" message and if so should return "Hallo Welt". The incoming side is working fine but I get no outgoing connection.

Now I don't know if the problem is within Docker, NodeRed or my visualization server. Both NodeRed and the server show the connection as established. I can receive a message "Hallo" and the flow wants to send out "Hallo Welt", but I do not receive any message on the KNX server.

I set the TCP in node to listen on port 1338 and the out node to "answer on TCP". The KNX server is a TCP client connecting to the Synology IP with the port set in Docker. In my case, I map 49157 (automatically generated) to 1338.

Now I know that this post is weirdly written, I am sorry for me being a German guy writing in English while still thinking in German :D