Hello there,  I was having the same issue, and it turned out to be a problem with the installation. So, I just did a yum remove splunk* and removed the /opt/splunkforwarder home directory completely.  After, uninstalling and removing the splunk home directory, and I started spunk just fine and I was able to run the add monitor command without any issues.  I'm running RHEL 8.x and issuing all of these commands via the Linux CLI. Splunk version is 9.1.2. I hope this helps.  Respectfully.  Guillermo  Washington, DC ... View more