Physics, The ball goes through the terrain

Questions
1

I use this simple code, see. below. The ball(sphere) falls on the ground(terrain). The ball actually falls but passes through the terrain. There will be no bounces. Where is the mistake? Thank you for your time.

if (evt.sourceEvent.key == “f”) {

            //scene.enablePhysics(null, new BABYLON.CannonJSPlugin());

            scene.enablePhysics(null, new BABYLON.OimoJSPlugin());

            terrain.physicsImpostor = new BABYLON.PhysicsImpostor(terrain, BABYLON.PhysicsImpostor.MeshImpostor, {mass: 0, friction: 0, restitution: 0.3});

            sphere.physicsImpostor = new BABYLON.PhysicsImpostor(sphere, BABYLON.PhysicsImpostor.SphereImpostor, {mass: 1});

    }