Setup Backup App/ Externer Speicher

Hi guys. Trying to figure out the setup for backing up my data from one Nextcloud installation to the other using the new Backup App/ External Storage under NC 23. I want to backup NC 1 to my NC 2. The NC2 is only accessible over abc.local/nextcloud.
So under “add storage” I choose “Nextcloud”, under “Foldername” I entered the name of the folder I created for this purpose on my NC2. Under “Authentication” I chose “username & password”. Under “Configuration” I entered URL “abc.local/nextcloud” (also tried the 192.168… or without the “/nextcloud”). There is also a field called “remote subfolder” (entfernter Unterordner) which I don’t really know what to do with it. Do I also have to enter the name of the folder I created under NC2? And then of course username and password (both definitely correct).
When I enter the information and click “check” it gives me a red exclamation mark.

Any ideas?