Unity Error when uploading the model

I get an error when uploading from Unity.

“An error Ocurred when Updating the model”

The log is:

400 HTTP/1.1 400 Bad Request
Sketchfab.SketchfabAPI:Update() (at Assets/Sketchfab For Unity/Scripts/SketchfabApi.cs:117)
Sketchfab.SketchfabPlugin:Update() (at Assets/Sketchfab For Unity/Scripts/SketchfabPlugin.cs:210)
Sketchfab.SketchfabExporter:Update() (at Assets/Sketchfab For Unity/Scripts/SketchfabExporter.cs:87)

What can i do or what am i doing wrong?

Is the model too complex?

Thank You Very Much!