onTriggerEnter not working

I just started unity a few days ago, and I realised that I cannot get the function “onTriggerEnter” working. My set up is simple, I created two 3D cube, one red, one purple. The red cube can be moved by keyboard. Once red cube enter the boundary of purple cube, the purple will be destroyed and print a line “entered” in the console. However, it is not working. Nothing is showing, when I collide the red cube into the purple one. The script attach to the purple cube is shown below, and I have checked the “is Trigger” option for the purple cube

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

public class enter : MonoBehaviour
private void onTriggerEnter(Collider other)

The “OnTriggerEnter” function needs to start with a capital “O”.

Do you have Rigidbody added? Both objects have colliders? Only one is in isTrigger mode?
Check documentation (especially the Note section) Unity - Scripting API: Collider.OnTriggerEnter(Collider)