NullReferenceException using GetComponent<>()

I don't quite understand why i keep receiving a NullReferenceException when using the code in script "ClickableObject"

 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;
  
 public class ClickableObject : MonoBehaviour, IPointerClickHandler
 {
     _GameControler gc;
 
     void start()
     {
         gc = GetComponent<_GameControler>();
     }
 
     public void OnPointerClick(PointerEventData eventData)
     {
         if (eventData.button == PointerEventData.InputButton.Left)
         {
            Transform currentChild = eventData.selectedObject.transform.GetChild(0);
            gc.ChangeButtonText(int.Parse(currentChild.name));
         }
     }
 }

To access the function in script "_GameControler"

 public void ChangeButtonText(int index)
     {
         Debug.Log(index);
     }

Both Scripts are attached to an empty GameObject in the editor

and running the script and activating the trigger for OnPointerClick returns this error

Can anyone tell me how I'm being dumb?