Entity clamp to tileset

I try clamping entities to DEM tileset . Entites have .glb models. As we could imagine, I wanna set the flags in custom terrain but terrain is 3d tileset.
I tried “clamp to 3d model” in the sandcastle but it was not.
Is there a way I can simply solve?

Welcome to the Cesium Community!

Can you share the Sandcastle you created here?