I suggest you look at Having problems with UrBackup? Please read before posting to see how to collect information from the server and see if there are any messages that offer clues to what is going on.
I would also check if a web browser on the server can use 127.0.0.1:55414 to connect with any better result.
Should you be using http or https?
You may get a better answer if you post the revision and version of the server system, the urbackup server version you use and the browser version that is failing.