I created a playground here https://playground.babylonjs.com/#QLH09X#3.
As you can see in the code, I used
BABYLON.PhysicsImpostor for both ground and box, but the box still just went through the ground.
I basically just follow this https://www.babylonjs-playground.com/#D3LQD#7
I’m sure it’s just a small thing that’s missing, but I just can’t spot it.
Thank you in advance.