Hello!
i got a little problem/project. I’m trying to “synchronize” my two Nextcloud Boxes with an Nextcloud server in an datacenter.
One of the Nextcloud Boxes will be placed at home and one in my office/at work. I already setup the boxes completly at home, i’m using a Raspberry PI3 with a static IPv4. Now my problem, the boxes are full acessable at home in my local network but not from outside of the network (tested with my smartphone).
I tried to use the Federation feature but i only works in one direction, i can share files from my local Nextcloud server to the datacenter Nextcloud server but not back to the local Nextcloud Box.
I always get this message"Sharing Myfile failed. could not find johndoe@web.de@localip maybe the server is currently unreachable or uses a self-signed certificate." (I changed the Federated-Cloud-ID because i don’t want to make it public.)
I don’t want to use a Domain, only my static IP of my Nextcloud Box and i m also using no certificate. I also opened the ports 80 and 433.
Sorry for my bad english.
I hope somebody can help me. 
Sincerely
Dominik