Onlyoffice integration, bad request or timeout

Hello there,
I am trying to integrate onlyoffice into my nextcloud. Everything is running in docker with the official images.
I have nextcloud running behind a nginx reverse proxy to get ssl encryption, port 80 is exposed inside the docker net only, the proxy uses port 8080. I now also set up an onlyoffice document server using a letsencrypt certificate, which also greets me "Thank you for choosing ONLYOFFICE!
Document Server is running"
The onlyoffice port 443 is directly accesable through port 8081.
The plugin is installed, but it does not work to just enter as address of the document server.
I think, the reason may be the inverse proxy. Any suggestions how to fix that?

So I know realize I simply cannot connect to my own server from within the image of docker that is running nextcloud:

curl: (7) Failed to connect to port 443: No route to host’

I am not sure how to fix that right now. I still use the nginx reverse proxy:

ssl-proxy: image: justsml/ssl-proxy:latest environment: - HTTPS_PORT=8080 - - UPSTREAM_TARGET=app:80 - CERT_PUBLIC_PATH=/certs/fullchain.pem - CERT_PRIVATE_PATH=/certs/privkey.pem - SSLProxyVerify=none - SSLProxyCheckPeerCN=off - SSLProxyCheckPeerName=off - SSLProxyCheckPeerExpire=off volumes: - /home/nextcloud/certs:/certs:ro links: - app ports: ['8080:8080']

Ok, you may close this. The issue is completly within my proxy. I just added onlyoffice to the docker network now and will have a look at the proxy. This way it works.