ws://backups.domain.com/socket instead of urbackup://backups.domain.com:80
and
wss://backups.domain.com/socket instead of urbackup://backups.domain.com:443
Using urbackup:// means it uses the “UrBackup” protocol directly and not HTTP.
If it doesn’t work enabling client debug logging and looking at the log file should help.
Depending on what you mean by proxy it might not work. The HTTP proxy isn’t used currently. (It might work if you mean using Treafik as proxy on the server)
For everyone like me that came across this post trying to do the same thing, I just wanted to show what worked for me.
The documentation says that the port for internet clients is 55415 but if you are using websocket (with a proxy for example) you need to use the same port as the web interface (In my case 55414)