Check if the license.txt file exists on the system
The default for the license.txt file is the /opt/syslog-ng/etc/ directory.
You can also run the following on Linux systems:
$ /opt/syslog-ng/sbin/syslog-ng-ctl show-license-info
The equivalent command on Windows Syslog-ng PE is:
C:\Program Files\syslog-ng\bin\syslog-ng-ctl.exe show-license-info >[OUTPUT_FILE]
If there is no license found, install one.
Syslog-ng will need to be restarted to find the license.