Help with SetPixels32

Hi everybody,

This is my first time using SetPixels32 and I'm running into an error that I can't understand. Basically right now what I want to do is change a square of "brushSize" length to red. This is my code:

 public class PaintingUVs : MonoBehaviour {
 
     [SerializeField]
     private int brushSize;
 
     private Color32[] pixelColorArray; // stores the pixel colors we'd like to paint
     void Start()
     {
         pixelColorArray = new Color32[brushSize * brushSize];
 
     }
 
     // Use this for initialization
     void OnGUI () {
         Event evt = Event.current;
         if (evt.isMouse && Input.GetMouseButton(0))
         {
             // Send a ray to collide with the plane
             Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
             
             if (Physics.Raycast(ray, out hit, Mathf.Infinity))
             {
                 // Find the u,v coordinate of the Texture
                 Vector2 uv;
                 uv.x = (hit.point.x - hit.collider.bounds.min.x) / hit.collider.bounds.size.x;
                 uv.y = (hit.point.y - hit.collider.bounds.min.y) / hit.collider.bounds.size.y;
                 // Get material
                 Texture2D tex = (Texture2D)hit.transform.gameObject.GetComponent<Renderer>().material.mainTexture;
 
                 if (tex != null)
                 {
                     // create a color array
                     for(int i =0; i < pixelColorArray.Length; i ++)
                     {
                         pixelColorArray[i] = Color.red;
                     }
                         Debug.Log("the pixel array is "+pixelColorArray.Length + " long. And our square is "+ (brushSize*brushSize).ToString() + " long");
                     tex.SetPixels32((int)(uv.x - brushSize/2), (int)(uv.y - brushSize/2), brushSize, brushSize, pixelColorArray);
                     tex.Apply(false);
                 }
             }
         }
     } //end method
 
 }
 

When trying to run I get a "SetPixels32 called with invalid number of pixels in the array" error. However the Debug.Log I use before the SetPixels method shows that the number of pixels in the array and the size of the square are the same. I've also tried setting brushSize to be the same as the texture size, but the error remains.

I think I must be misunderstanding how SetPixels32 works, in my mind, this code should allow you to draw a red square in the texture with a single click. Anyone knows why this error is appearing?

Thanks in advance.