Unity custom spawn handler not calling ?

I followed Unity Custom Spawn Handler to implement Object pooling https://docs.unity3d.com/Manual/UNetCustomSpawning.html. But in my case Spawn Handler function is not working on the client side. So what could be the reasons that Spawn handler function is not working?

Code: Spawn Manager

Code (CSharp):

1. public class SPawn : MonoBehaviour {
2.     public int m_ObjectPoolSize = 10;
3.     public GameObject m_Prefab;
4.     public GameObject[] m_Pool;
5.  
6.     public NetworkHash128 assetIDBullet { get; set; }
7.  
8.     public delegate GameObject SpawnDelegate(Vector3 position, NetworkHash128 assetId);
9.     public delegate void UnSpawnDelegate(GameObject spawned);
10.  
11.     void Start() {
12.         assetIDBullet = m_Prefab.GetComponent<NetworkIdentity>().assetId;
13.         m_Pool = new GameObject[m_ObjectPoolSize];
14.         for (int i = 0; i < m_ObjectPoolSize; ++i) {
15.             m_Pool[i] = (GameObject)Instantiate(m_Prefab, Vector3.zero, Quaternion.identity);
16.             m_Pool[i].name = "PoolObject" + i;
17.             m_Pool[i].SetActive(false);
18.         }
19.  
20.         ClientScene.RegisterSpawnHandler(assetIDBullet, SpawnObject, UnSpawnObject);
21.     }
22.  
23.     public GameObject GetFromPool(Vector3 position) {
24.         foreach (var obj in m_Pool) {
25.             if (!obj.activeInHierarchy) {
26.                 Debug.Log("Activating GameObject " + obj.name + " at " + position);
27.                 obj.transform.position = position;
28.                 obj.SetActive(true);
29.                 return obj;
30.             }
31.         }
32.         Debug.LogError("Could not grab GameObject from pool, nothing available");
33.         return null;
34.     }
35.  
36.     public GameObject SpawnObject(Vector3 position, NetworkHash128 assetId) {
37.         return GetFromPool(position);
38.     }
39.  
40.     public void UnSpawnObject(GameObject spawned) {
41.         Debug.Log("Re-pooling GameObject " + spawned.name);
42.         spawned.SetActive(false);
43.     }
44. [B]In the previous code The SpawnManager class the Handler function SpawnObject is not working on client but UnSpawnObject is working.[/B]
45. }

Code: Player

Code (CSharp):

1. using System.Collections;
2. using UnityEngine;
3. using UnityEngine.Networking;
4.  
5. public class Play : NetworkBehaviour {
6.  
7.     SPawn spawnManager;
8.  
9.     void Start() {
10.         spawnManager = GameObject.Find("SP Manager").GetComponent<SPawn>();
11.     }
12.  
13.     void Update() {
14.         if (!isLocalPlayer)
15.             return;
16.  
17.         var x = Input.GetAxis("Horizontal") * 0.1f;
18.         var z = Input.GetAxis("Vertical") * 0.1f;
19.  
20.         transform.Translate(x, 0, z);
21.  
22.         if (Input.GetKeyDown(KeyCode.Space)) {
23.             // Command function is called on the client, but invoked on the server
24.             CmdFire();
25.         }
26.     }
27.  
28.     [Command]
29.     void CmdFire() {
30.         // Set up coin on server
31.         var coin = spawnManager.GetFromPool(transform.position - transform.right);
32.         coin.GetComponent<Rigidbody>().velocity = transform.forward * 4;
33.  
34.         // spawn coin on client, custom spawn handler is called
35.         NetworkServer.Spawn(coin, spawnManager.assetIDBullet);
36.  
37.         // when the coin is destroyed on the server, it is automatically destroyed on clients
38.         StartCoroutine(Destroy(coin, 2.0f));
39.     }
40.  
41.     public IEnumerator Destroy(GameObject go, float timer) {
42.         yield return new WaitForSeconds(timer);
43.         spawnManager.UnSpawnObjectBullet(go);
44.         NetworkServer.UnSpawn(go);
45.     }
46. }
47.  

 

Well, I don't know how but, it worked. I simply removed gameObject prefab from NetworkManager's Registered Spawnable Prefab and the SpawnHandler worked. Now can anyone explain to me why this worked?