Selfhosted Docker - Custom DNS (Alternate URL) not working.

[kiroubel-girma]

I have a Docker installation (ONLYOFFICE DocSpace v 1.1.1).
Things work OK with default local IP address URL ( i.e. http://192.168.0.113).
What I want is to use the fully qualified domain name.
I enabled "DNS Settings", and under "Custom Domain Name" I entered the FQDN (docspace.example.com).
But value is not used at all. Emails still show the IP address. Invite links also use the IP address URL.

Note that what I really want is to specify an alternate base URL to use (i.e. https://docspace.example.com)
That's because I use a reverse proxy to access the site securely.