My attempt:
$ sudo yunohost app install https://github.com/duniter/duniter_ynh
Available domains:
- xxx.net
Dedicated domain name on which no application must be installed. Install will be done on root path. (default: xxx.net):
Administrator. Must a YunoHost user.: xxx
Warning: 'yunohost app checkurl' is deprecated and will be removed in the future
Warning: Unable to install the app in this location
Warning: Path not available: xxx.net/
Warning: sudo: duniter: command not found
Warning: dpkg: warning: ignoring request to remove duniter which isn't installed
Warning: Unknown service 'duniter'
Warning: usage: yunohost firewall disallow {TCP,UDP,Both} port
Warning: [-h] [-4] [-6] [--upnp-only] [--no-reload]
Warning: yunohost firewall disallow: error: too few arguments
Warning: duniter has not been properly removed
Success! The SSOwat configuration has been generated
Error: Installation failed