How to detect collision of a wall with grid movement?

Hi everybody

I have this little game, where my player is moving around a simple level, using a grid based movement script (See code below). My problem is that I have tried to implement a 2D raycast, which has to detect if the next 'tile' is a movable tile (not a wall). However all the examples I have found on the internet hasn't been something I could make work. So please help me with how I can detect if the player is allowed to move, before he moves.

 using System.Collections;
 using UnityEngine;
 
 public class GridMove : MonoBehaviour {
     public float moveSpeed = 2f;
 
     private float gridSize = 1f;
     private enum Orientation {
         Horizontal,
         Vertical
     };
     private Orientation gridOrientation = Orientation.Vertical;
     private bool allowDiagonals = false;
     private bool correctDiagonalSpeed = true;
     private Vector2 input;
     private bool isMoving = false;
     private Vector3 startPosition;
     private Vector3 endPosition;
     private float t;
     private float factor;
     private Animator animator;
 
     // Use this for initialization
     void Start () {
         animator = GetComponent<Animator>();
     }
     
     public void Update() {
         if (!isMoving) {
             input = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
             if (!allowDiagonals) {
                 if (Mathf.Abs(input.x) > Mathf.Abs(input.y)) {
                     input.y = 0;
                 } else {
                     input.x = 0;
                 }
             }
 
             if (input != Vector2.zero) {
                 StartCoroutine(Move(transform));
                 animator.SetBool("isWalking", true);
             }
             else {
                 animator.SetBool("isWalking", false);
             }
         }
     }
     
     public IEnumerator Move(Transform transform) {
         isMoving = true;
         startPosition = transform.position;
         t = 0;
 
         animator.SetFloat("x", input.x);
         animator.SetFloat("y", input.y);
         
         if(gridOrientation == Orientation.Horizontal) {
             endPosition = new Vector3(startPosition.x + System.Math.Sign(input.x) * gridSize,
                                       startPosition.y, startPosition.z + System.Math.Sign(input.y) * gridSize);
         } else {
             endPosition = new Vector3(startPosition.x + System.Math.Sign(input.x) * gridSize,
                                       startPosition.y + System.Math.Sign(input.y) * gridSize, startPosition.z);
         }
         
         if(allowDiagonals && correctDiagonalSpeed && input.x != 0 && input.y != 0) {
             factor = 0.7071f;
         } else {
             factor = 1f;
         }
 
         while (t < 1f) {
             t += Time.deltaTime * (moveSpeed/gridSize) * factor;
             transform.position = Vector3.Lerp(startPosition, endPosition, t);
             yield return null;
         }
         
         isMoving = false;
         yield return 0;
     }
 }