Here is the steps to add a custom domain:
1. Add an A record using your DNS provider for example rutorrent.example.com pointing to your appbox IP (found on https://www.appbox.co/appboxmanager/appboxes)
2. Make sure if you're using CloudFlare that proxying is disabled and the orange cloud icon for the record is grey
3. Go to https://www.appbox.co/appboxmanager/domains and add just the base domain (not the subdomain) for example: example.com
4. Go to the app store, select the app you wish to install
5. Set the domain field to your custom domain, for example: example.com
6. Set the subdomain field to whatever you want to use for the first part of the domain, for example if you wanted rutorrent.example.com, you would set the subdomain field to rutorrent
