The Administration Manual for UrBackup Server 2.5.x in Sub-Section 8.1.2 Server URL of Section 8 Server settings states that URLs take the form of
http://backups.company.com:55414/
In troubleshooting my first attempt at backing up remote clients (to a Docker-based UrBackup app—Version 1.1.6—running on TrueNAS Scale 25.10.7) I found that I had to omit the trailing slash, in order to not get a “The server port is not valid” error.
Elsewhere I saw a URL using “urbackup” in the protocol part of the URL. urbackup://backups.company.com:55414 was no improvement, however. The client still could not connect to the server through an internet connection.
When trying to add the client to the server again through the “Add new client” button on the Status page of the UrBackup web interface, I chose the “Add new Internet/active client” section and clicked on the “Add client” button.
Studying the resultant page I took note of the instructions following the bullet point “Alternatively after you installed the client from: https://www.urbackup.org/download.html”. The key was to use the authentication key, which goes into the “Internet server password” field of the Internet tab of the UrBackup client, and the URL, ws://hostname.net:55414/socket, which goes into the “Server URL client connects to” field on the same tab.
Unless there were other mistakes I made in going from a failed to a working configuration that kept the client from backing up to the server, I propose that the manual should be updated with an example of a ws://… URL.