Parameter 'Walk' doesn't exist?

I'm trying to make walk animation. But when I try to change animation idle to walk, ıt doesn't work. It says 'Parameter "Walk" doesn't exist'but I added parameter and script works. I can manually change parameter and it works(walk animation is playing). But when I try to change via script, ıt doesn't work.

Here are codes

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Controller : MonoBehaviour
 {
 
     private Rigidbody rb;
 
     private float xPos;
 
     Vector3 playerMovement;
 
     [SerializeField] Animator anim;
     
     
     
 
 
     private void Awake() => rb = GetComponent<Rigidbody>();
 
     private void Start()
     {
 
         
         xPos = transform.position.x;
 
     }
 
 
 
 
 
 
 
 
     // Update is called once per frame
     void Update()
     {
         Move();
         
     }
 
     private void Move()
     {
         
         float mH = Input.GetAxis("Horizontal");
 
          playerMovement = new Vector3(0, 0, mH);
 
         rb.AddForce(playerMovement * 2f);
 
         anim.SetFloat("Walk", 1);
 
         transform.position = new Vector3(xPos, transform.position.y, transform.position.z);
         
 
     }
 
 
     
 }