Emoncms Android App Connection Error

I am having prblems getting the android app to connect to my emoncms

I am running emoncms in docker on a synology DSM. I have no problem connecting when using local ip, but when I try to connect from outside my network I am getting a connection error message in the App

I am using Duck DNS for DDNS and a reverse proxy in synology DSM to point to the emoncms ip & port.

The remote login works on a web browser, but not the Android app.