SketchUp Mobile Viewer (Which Option)

Hi,

I just bought SketchUp Mobile Viewer and i have connected my Dropbox to it… however when i go to open a file from Dropbox it does not find any SketchUp 3D models.

I exported two models (file types) to my dropbox and i can see them in my Dropbox app itself, but i SketchUp Mobile Viewer is not seeing them.

What file format should they be in? Thanks in advance for your help.