Nextcloud federation

I have two nexcloud one internal and external
i connect the internal to external and i share folder when i go to external i add it in file but when i access to file show me this error " Page not found

The page could not be found on the server or you may not be allowed to view it."

The servers are in the same network? Can they see each other?

Logfiles would be interesting, also which versions are you using? Are you passing through reverse proxies?