How to fix Filepath selected, but couldn't find any humans

This error occurs when you have entered a filepath for Human Generator's content packs, but the add-on can't find the files containing the human 3D models in this path.

Please select one of the following:

1. This is the first time I'm installing Human Generator on this computer
2. I have just updated Blender or Human Generator to a new version

When installing Human Generator for the first time: