"The package "@frontity/my-first-theme" doesn't seem to be installed"

Hi all. I’m trying to work with the tutorial

I’ve hit an issue when following the instructions on this page:

When do “npx frontity dev”, I get the error:
“The package “@frontity/my-first-theme” doesn’t seem to be installed”

This is after I’ve followed the previous steps, and create the “my first theme” project.
The project exists under the ‘packages’ directory.
The directory under packages is named ‘my-first-theme’.
The package.json file within that directory has the name/value pair: ‘name’, ‘my-first-theme’.

What could be the issue here?