At present no data populates (get Oops! error message) when only Amazon is selected in the Geography selections. If however, another channel is selected such as "Total US-Natural Channel" the Amazon data does populate. There may be times when a client wants to focus solely on Amazon data or a particular channel.
This is certainly a usability issue, will raise with PoC team to investigate ALTHOUGH I believe key insights will still be available with the workaround of adding another geo.