Hello @hendryman
If you have installed spx successful but you can not run it, it seems like there is something wrong with your environment var - PATH, especially you are using z shell.
I have seen a thread which mentioned similar problem and I think you may want to take a look - https://stackoverflow.com/questions/18428374/commands-not-found-on-zsh
If you still have this issue after set the PATH well, please let us know, we are glad to help you raise a support ticket to investigate your local environment.
Looking forward to your response and I hope this helps.
Regards,
Yutong