An error in the code in physics 2d and overlapcircle, what should I do?

Question

C++ / C#

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

public class PlayerContorller : MonoBehaviour
{
    public float speed;
  public float JumpForce;
  private float moveInput;
  
  private Rigidbody2D rb;
  
  private bool facingRight = true;
  
  private bool isGrounded;
  public Transform feetPos;
  public float checkRadius;
  public LayerMask whatIsGround;
  
  private void Start()
  {
    rb = GetComponent<Rigidbody2D>();
  }
  
  private void FixedUpdate()
  {
    moveInput = Input.GetAxis("Horizontal");
    rb.velocity = new Vector2(moveInput * speed, rb.velocity.y);
    if(facingRight == false && moveInput > 0)
    {
      Flip();
    }
    else if(facingRight == true && moveInput < 0)
    {
      Flip();
    }
  }
  
  private void Update()
  {
    isGrounded = Physics2D.OverLapCircle(feetPos.position, checkRadius, whatIsGround);
    
    if(isGrounded == true && Input.GetKeyDown(KeyCode.Space))
    {
      rb.velocity = Vector2.up * jumpForce;
    }
  }
  
  void Flip()
  {
    facingRight = !facingRight;
    Vector3 Scaler = transform.localScale;
    Scaler.x *= -1;
    transform.localScale = Scaler;
  }
}

I don't understand where is the error, please help!