On the Sketchup Pricing page ( https://www.sketchup.com/buy/pricing ), in the Sketchup Free column there is an Interoperability row. In the Interoperability > Free row is says Basic (with a small i).
When you move your mouse over the i it says Supported File Types.
FBX is listed as one of the Supported File Types. Yet when using Sketchup Free and choosing export there is a padlock and an upgrade button.
Can Sketchup Free Online export FBX files?