Trying to create a Sierra restore drive, Instead I get "/Volumes/MyVolume is not a valid mount point."

I have a used Mac mini with an untrusted install of Sierra upgraded from Lion, thereby activating that security chip to stop me from using Recovery mode to roll back to an new install of Lion and back up via the download from Apple.

I formatted my flash drive as MacOS Extended with the volume name of /MyVolume and followed the instructions on https://support.apple.com/en-us/HT201372 to the letter, copy and pasting the code for

Sierra into my terminal.

Instead of working, all I keep getting is "/Volumes/MyVolume is not a valid mount point." I left feedback describing this on the support article and got directed to a discussion with multiple copies of that exact same code, all claiming to work where this code doesn't and all giving the exact same error message instead of working.

Only thing on that thread that might have been helpful was a link to a third-party app downloadable from an unknown third-party website to do the job. Not an option.

I've re-initialized the flash drive, typing in the matching volume name each time, and still get the same error: "/Volumes/MyVolume is not a valid mount point."

This used computer may never get a copy of OS X that hasn't already been used on a retired Mac I had.