maybe this can help : https://forum.mendix.com/link/space/marketplace/questions/117458
I just encountered the same problem and still don't know the solution
However there is a workaround:
1. Download the 3D Viewer sample app
2. Open in Mendix Studio and export the 3DViewer module
3. Import this module into your app
Another workaround is to get hold of the following jar files and add them to your userlib folder manually: