Why doesn't contact work in unity?

Question

C++ / C#

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

public class Transform : MonoBehaviour
{   
    
    public float groundCheck = 1f;
    // Start is called before the first frame update
    void Start()
    {
        transform.position = new Vector3(0,0,0);
    }
    
    void onCollisionEnter2D(Collision2D other){
    	if(other.gameObject.tag == "Finish"){
    		groundCheck = 0f;
    		print("afafa");
    	}
    }
    // Update is called once per frame
    void Update()
    {   
    	if (Input.GetKey(KeyCode.D)){
    	transform.position += new Vector3(0.1f, 0, 0);
        }

        if(Input.GetKey(KeyCode.A)){
        transform.position -= new Vector3(0.1f, 0, 0);
        }

        if(Input.GetKey(KeyCode.W)){
        	if(groundCheck == 0){
              transform.position += new Vector3(0, 1, 0);
              groundCheck = 1f;
         }
       }
    }
}