Splunk installed failed to create splunk account on RHEL

Dear experts, I installed splunk on the rhel servers. Majority of the time it works fine. But for this one server, when I tried to change ownership of a directory, chown -R splunk:splunk ./***deploymentclient/

it says

chown: invalid user: `splunk:splunk'

Can someone please tell me why the splunk install failed to create a splunk account on the machine?

And how do I resolve this? is it a simple useradd, etc?

Thanks,