How do I fix "Failed to listen on prefix" error when starting Remote Access Server?

If you see an error stating "Failed to listen on prefix 'https://+:25433/' because it conflicts with an existing registration on the machine" when trying to start the Remote Access Server, this means another application is already using that port number.

To resolve this issue, click Advanced in the Configure Remote Access Server window. Change the Open remote connection on port field to a different port number (for example, 25434 or any unused port above 1024). Once you've changed the port, click Start Server to restart the service.

After changing the port, you'll also need to update your firewall rules and port forwarding settings to use the new port number. You can use the Create rule button to automatically update your Windows Defender firewall rule, and refer to the port forwarding helper under Help me set up external connections to update your router configuration.