Today I bought Qimage one and installed it on my MacBook Pro running High Sierra OS (Up to date) and my adobe LR/PS is uptodate, when I started the program it gave me this error message:

"The Qimage One Adobe plugin could not be installed in the directory below. Please check the permissions on the Plug-ins directory.

/Applications/Adobe Photoshop CC 2018/Plug-ins/Qimage One"

Sure enough it was not installed on PS however the plugin is on LR and accessible.
I tried to reinstall it...Same thing
copy the plugin from the Qimage resource folder to the PS plugin folder gets it to work but with the same message, and am not sure if the export plugin needs to be copied there too?
I should not have to do that manually.
it was Qimage-One-v2018.117.pkg

I'm still here.  There are manual installation instructions that should work in the event the plugins cannot be installed automatically.  I'm not sure which version of Qimage One you are using but in the Windows version, you cango to Utilities, Explore Qimage Application Data, and the instructions are in the Plugins folder (Lightroom or Photoshop subfolders).

Regards,
Mike