The command 'pbsnodes - l free' in PBS Pro v19.1.3 cannot be used

The command ‘pbsnodes - l free’ in PBS Pro v19.1.3 cannot be used.
The prompt is as follows:
usage: pbsnodes [-{o|r}][-C comment][-s server] host host …
pbsnodes -l [-s server]
pbsnodes [-s server] -v vnode vnode …
pbsnodes -a[v][S[j][L]][-F format][-D delim][-s server]
pbsnodes -[H][S[j][L]][-F format][-D delim] host host …
pbsnodes --version
Why?
Is there a way to make the command ‘pbsnodes - l free’ usable.
Thank you!!!