Docker-nextcloud: Adding onlyoffice-document-server - Unknown error

I am replying to him because this topic, that he started, is about getting it to work with Traefik. And he posted he got it working:

(…) I had to adopt the header config since I’m using traefik as the edge-router instead of nginx based on this post

The post he is referring to, I have no clue how he used that information to change his setup.