My character can Only Jump Once

Hello, it's me again. I fixed the last error with the help of you guys. Anyways, while I was testing my game, I realized I could only Jump once in my game. I made sure I tagged my baseplate as Ground, and I made sure my script wa right. Yet I couldn't find a solution. Could you guys help me again?
Here is the code for the jumping.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using TMPro;
5.  
6. public class PlayerControls : MonoBehaviour
7.  
8. {
9.     public float speed = 15f;
10.  
11.     private Rigidbody rb;
12.  
13.     public float jumpForce = 14;
14.  
15.     public bool cubeIsOnTheGround = true;
16.  
17.     public TextMeshProUGUI ScoreText;
18.     private int Score;
19.  
20.  
21.     // Start is called before the first frame update
22.     void Start()
23.     {
24.         rb = GetComponent<Rigidbody>();
25.     }
26.  
27.     // Update is called once per frame
28.     void Update()
29.     {
30.         PlayerRun();
31.         if (Score >= 3)
32.         {
33.  
34.             YouWin();
35.         }
36.  
37.     }
38.  
39.  
40.     void YouWin()
41.     {
42.         ScoreText.text = "You win";
43.         Time.timeScale = 0f;
44.     }
45.  
46.  
47.     void PlayerRun()
48.     {
49.  
50.         float leftRight = Input.GetAxis("Horizontal");
51.         float forwardBack = Input.GetAxis("Vertical");
52.         Vector3 CharacterMove = new Vector3(leftRight, 0, forwardBack) * speed * Time.deltaTime;
53.         transform.Translate(CharacterMove, Space.Self);
54.  
55.         if (Input.GetButtonDown("Jump") && cubeIsOnTheGround)
56.         {
57.  
58.             rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);
59.             cubeIsOnTheGround = false;
60.         }
61.         void OnCollisionEnter(Collision collision)
62.         {
63.             Debug.Log("Entered");
64.             if (collision.gameObject.tag == ("Ground"))
65.             {
66.                 cubeIsOnTheGround = true;
67.  
68.             }
69.         }
70.     }
71.  
72.     void OnTriggerEnter(Collider other)
73.     {
74.         if (other.gameObject.CompareTag("Item"));
75.         other.gameObject.SetActive(false);
76.         AddScore();
77.     }
78.  
79.  
80.  
81.  
82.  
83.     void AddScore()
84.     {
85.         Score++;
86.         ScoreText.text = Score.ToString();
87.  
88.     }
89. }

 

I think that OnCollisionEnter(Collision collision) will never be called because you nested it inside PlayerRun().
I didn't even know that is possible in c#

 

Its a pretty new feature in C#. Itsd actually pretty usable. for things like

Code (CSharp):

1. public void OuterMethod(foo)
2. {
3.    State GetState()
4.    {
5.       if(someCondition) return someState;
6.       if(someOtherCond) return someOtherState;
7.      
8.       return someDefaultState;
9.    }
10.  
11.    var state = GetState();
12.    ...
13. }