Missing objects, pls help

Hi, everyone!
I'm new to Unity and I have a task of creating an object that appears upon tap. I'm working along this tutorial:

The problem is that when I just place a cube, bulid&run, the cube appears floating, just like in the tutorial. Than I create a placement indicator and follow along the tutorial with code.

When I finish it, hit build&run, both placement indicator and the object disappear. They're visible before I attach the C# script. What am I missing? I re-wrote the code by hand to make sure everything is where is should be. Tried everything I could think of and still the same result - empty device viewport.
Pls help.

The code is here:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.XR.ARFoundation;
5. using UnityEngine.Experimental.XR;
6. using System;
7.  
8. public class ARTapToPlaceObject : MonoBehaviour
9. {
10.     public GameObject objectToPlace;
11.     public GameObject placementIndicator;
12.  
13.     private ARSessionOrigin arOrigin;
14.     private Pose placementPose;
15.     private bool placementPoseIsValid = false;
16.  
17.     void Start()
18.     {
19.         arOrigin = FindObjectOfType<ARSessionOrigin>();
20.     }
21.  
22.     void Update()
23.     {
24.         UpdatePlacementPose();
25.         UpdatePlacementIndicator();
26.  
27.         if (placementPoseIsValid && Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began)
28.         {
29.             PlaceObject();
30.         }
31.     }
32.  
33.     private void PlaceObject()
34.     {
35.         Instantiate(objectToPlace, placementPose.position, placementPose.rotation);
36.     }
37.  
38.     private void UpdatePlacementIndicator()
39.     {
40.         if (placementPoseIsValid)
41.         {
42.             placementIndicator.SetActive(true);
43.             placementIndicator.transform.SetPositionAndRotation(placementPose.position, placementPose.rotation);
44.         }
45.         else
46.         {
47.             placementIndicator.SetActive(false);
48.         }
49.     }
50.  
51.     private void UpdatePlacementPose()
52.     {
53.         var screenCenter = Camera.current.ViewportToScreenPoint(new Vector3(0.5f, 0.5f));
54.         var hits = new List<ARRaycastHit>();
55.         arOrigin.Raycast(screenCenter, hits, TrackableType.Planes);
56.  
57.         placementPoseIsValid = hits.Count > 0;
58.         if (placementPoseIsValid)
59.         {
60.             placementPose = hits[0].pose;
61.  
62.             var cameraForward = Camera.current.transform.forward;
63.             var cameraBearing = new Vector3(cameraForward.x, 0, cameraForward.z).normalized;
64.             placementPose.rotation = Quaternion.LookRotation(cameraBearing);
65.         }
66.     }
67. }