Raycast not working properly

Hi I doing the 2d puzzle game that the player will flip to the ceiling when press the spacebar but the the bool I use was always turn to true every time. I want when the player was grounded than the player can flip and if not the player can't flip. I also want the player can't move when the flip here my code

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

public class PlayerController : MonoBehaviour { float horizontalMove; bool isJumping; RaycastHit2D hit;

 private Transform playerTransform;
 private Rigidbody2D playerRb2d;
 [SerializeField] float speed = 10f;
 PlayerController playerController;

 public float maxRayDistance = 5f;
 public LayerMask whatIsFlip;
 public bool isGrounded;
 public bool isWin;

 // Start is called before the first frame update
 void Start()
 {
     Cursor.lockState = CursorLockMode.Locked;

     playerTransform = GetComponent<Transform>();
     playerRb2d = GetComponent<Rigidbody2D>();
     playerController = GetComponent<PlayerController>();
 }

 // Update is called once per frame
 void Update()
 {
     horizontalMove = Input.GetAxis("Horizontal") * speed;
     isJumping = Input.GetButtonDown("Jump");

     Move();

     if (isJumping && isGrounded)
     {
         playerRb2d.gravityScale *= -1;
     }
 }

 private void FixedUpdate()
 {
     if(Physics2D.Raycast(playerTransform.position, Vector2.down, maxRayDistance, whatIsFlip))
     {
         isGrounded = true;
     }
 }

 void Move()
 {
     if (!isJumping)
     {
         playerRb2d.velocity = (transform.right * horizontalMove) + (transform.up * playerRb2d.velocity.y);
     }

     if (isJumping)
     {
         horizontalMove = Input.GetAxis("Horizontal") * 0;

         playerRb2d.velocity = (transform.right * horizontalMove) + (transform.up * playerRb2d.velocity.y);
     }
 }

 private void OnCollisionEnter2D(Collision2D other)
 {
     if(other.gameObject.CompareTag("Finish"))
     {
         isWin = true;
         playerController.enabled = false;
     }

     else
     {
         isWin = false;
     }
 }

}

hope someone can tell me the mistake that i made