If your server doesn't start, look at the main server log file /var/log/rport/rportd.log first. This can be done with a text editor or with the tail command. For example,
tail -n 200 /var/log/rport/rportd.log shows the last 200 lines.
Sometimes critical errors occur before the rport server can write log to its log file. These errors are usually logged through systemd. Use journalctl -u rportd.service -e --no-pager to inspect them.
If the above doesn't provide you enough information to understand why your server is not starting, try to run rportd without systemd in the foreground, which will print errors directly on your console.
# Run rportd in foreground
su - rport -s /bin/bash -c "/usr/local/bin/rportd -c /etc/rport/rportd.conf"
Share diagnostic data with the support
If you want to share diagnostic data with the RealVNC support, add the relevant files to an encrypted ZIP file and upload for later download.
The above command will ask for an encryption password. Provide a secure password and confirm. After the upload is completed, a download URL staring with https://transfer.sh is printed on the console. Share this URL and the password with the support engineer.