Thanks for the clarification.
Normally, you should see the authorization pop up when establishing a remote connection, if the Viewer had successfully reached the intermediary server (our public ID server or your self-hosted RU Server) and then had successfully established a connection to the Host through the intermediary server. In this case, I might assume that the issue occurs somewhere on these steps.
The troubleshooting guide would be helpful in order for us to isolate the issue. However, you might send us the Host and Viewer log files for examination.
Here's how you can locate the Host logs
and Viewer logs
You can send the log files to email@example.com
Please, do not publish the logs on the forum as they are considered personal information.
Looking forward to your reply.