I’m fairly new to unity, and I tried making a 2d platformer game. For some reason, the player only jumps sometimes when I press the spacebar but sometimes it doesn’t. Does anyone have any idea how I can fix this?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
    public float speed;
    private float Move;

    public bool isJumping;

    public float jump;
    public Vector2 boxSize;
    public float castDistance;

    private Rigidbody2D rb;
    public LayerMask groundLayer;

    bool grounded;
    // Start is called before the first frame update
    void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    // Update is called once per frame
    void Update()
    {
        Move = Input.GetAxis("Horizontal");

        rb.velocity = new Vector2(speed * Move, rb.velocity.y);

        if (Input.GetButtonDown("Jump") && isGrounded())
        {
            rb.AddForce(new Vector2(rb.velocity.x, jump));
            Debug.Log("jump");
        }
    }

    public bool isGrounded()
    {
        if (Physics2D.BoxCast(transform.position, boxSize, 0, -transform.up, castDistance, groundLayer))
        {
            return true;
        }
        else 
        {
            return false;
        }
    }

    private void OnDrawGizmos()
    {
        Gizmos.DrawWireCube(transform.position - transform.up * castDistance, boxSize);
    }

I tried to figure out what was wrong, and I figured out that it had something to do with the ground check true/false but I can’t figure out where.