Connect from one installation of NC to another

Hi all,

I’d like to move files from one NC installation to another, but can not add NC installation 15.0.12 to 16.0.5 NC installation via external storage.
Connection fails without any service message.
Both installations are on the same virtual server.
The NC to which I try to connect to has valid SSL sertificate.
I tried Nextcloud and WebDAV types of external webstorage, but both failed.

My system is
Nextcloud version: 15.0.12 and 16.0.5
Operating system and version: Debian 9.9
Nginx version: 1.14.1
PHP version 7.0.33 (15.0.12) and 7.2.17(16.0.5):

Are there any specific requirements to make such a connection successful?

You should enable federated sharing (on the admin page there are a few options regarding sharing). Did you check your logfile for messages? Have these setups different domains and subdomains or are they in different subfolders?