SOLVED: Problem installing via ASUSTOR App Central

[MrAtoz]

Update: Working with the maintainer of the App Central Jellyfin package, I was able to resolve this. The problem was that I was trying to launch Jellyfin from the ASUSTOR ADM running over HTTPS, but Jellyfin wasn't configured to accept HTTPS requests. 

Solution:

1. Log into ADM over HTTP
   
2. Start Jellyfin
   
3. Do basic Jellyfin configuration
   
4. Configure Jellyfin to use HTTPS
   
5. Reboot the NAS
   

After this, I was able to log into Jellyfin the usual way over HTTPS.