Why is my model not loading correctly? I attempted to make a simple cup for use in Tabletop Simulator.

When I load the .obj into the game, my model is missing an entire face (The bottom).

http://i.imgur.com/msNqasE.png

However I've uploaded the obj to the A360 viewer by Autodesk and it looks fine.

https://a360.autodesk.com/viewer/id/dXJuOmFkc2sub2JqZWN0czpvcy5vYmplY3Q6YTM2MHZpZXdlci90MTQ1OTIzMDk3MTkzMV8wOTc0NTM0Njk5NTExNjM1MS5vYmo%3D?designtype=obj

I just started using Blender today so theres a good chance I made a simple mistake.
The face is there but it faces the wrong direction. The autodesk viewer probably ignores the face normal and shows it on both sides.

What you have to do is to flip the normal of this face.

you can read more about this issue here:

How to make all faces flip to the right/consistent direction?