both systems (even running on the same machine) must resolve each other using right DNS records (sometimes DNS or access local resources through public URL is an issue - search for “rebind protection”) .
running
-
https://collabora.xyz/hosting/discoveryfrom the client -
curl https://nextcloud.xyz/loginand curl https://collabora.xyz/hosting/discovery
on your server might help to isolate the issue. Check this #Nextcloud forum topic and references for further insights