Chrome Version: 66.0.3359.10
OS: 10452.1.0
Chromebox Panther

What steps will reproduce the problem?
(1) Go to Downloads (filesystem)
(2) Click on "Add new services" next to "Recent" 
(3) Click on "Install new from the webstore"
(4) In the "Available services" select "UPshow" from horacio
(5) Click on "Add app" from the popup.

What is the expected result?
Its possible to Install the App

What happens instead?
Pop-up "Installation failed"

100% Reproducible.