OnTriggerEnter2d Not working

this is my script
using UnityEngine;
using System.Collections;

public class CheckpointScript : MonoBehaviour {

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {

}

void OnTriggerEnter2d(Collider2D collider){
	Debug.Log ("collide detected");
}

}

Wow this was so dumb it’s suppose to be OnTriggerEnter2D. the “d” is cap