Client connected, Auth error, serverpasswords identical

So I have set up Urbackup so that the clients connect to the server (Internet mode), the client says it is connected to the internet server but the debug log (of the client) shows that there is an authenication error. I compared the Internet server password in the client with the one recorded in the server (Settings, select client, Internet) and they are identical. I even overwrote the client pw by hand and with copy-paste. Still I get an authentification error.

2020-05-14 16:13:24: Trying to connect to internet server "" at port 55415
2020-05-14 16:13:24: Successfully connected.
2020-05-14 16:13:25: Error reading id of authentication response
2020-05-14 16:13:25: InternetClient: Had an auth error

On the server side, you cannot start any backup with the webUI and I am figuring out how to get debug level loggingg on the docker container that runs UrBackup. When I get the log I will edit this post.

If you have ideas what could fix the issue I would appreciate your answers. Thanks in advance