What is the difference between these two scripts?

I am following a tutorial to make a simple 2d shoot 'em up. If I type out the script myself it does not work but if I copy and paste the script everything works as expected. The non-working script never seems to call OnTriggerEnter2d because I tried putting in print statements but they never appear. The only differences I can find are different placement of brackets, spaces and comments but I see no reason for differing behavior. This has been driving me up the wall and I would greatly appreciate any explanation for the differences in behavior between these 2 scripts.

Not working:

 using UnityEngine;
 
 public class HealthScript : MonoBehaviour
 {
     public int hp = 1;
     public bool isEnemy = true;
     public void Damage (int damageCount)
     {
         hp -= damageCount;
 
         if (hp <= 0)
         {
             Destroy(gameObject);        
         }
     }
 
     void OnTriggerEnter2d(Collider2D otherCollider)
     {
         ShotScript shot = otherCollider.gameObject.GetComponent<ShotScript>();
         if (shot != null)
         {
             if (shot.isEnemyShot != isEnemy)
             {
                 Damage (shot.damage);
                 Destroy(shot.gameObject);
             }
         }
     }
 }
 

Working:

 using UnityEngine;
 
 public class HealthScript : MonoBehaviour
 {
     public int hp = 1;
     public bool isEnemy = true;
     public void Damage(int damageCount)
     {
         hp -= damageCount;
         
         if (hp <= 0)
         {
             Destroy(gameObject);
         }
     }
     
     void OnTriggerEnter2D(Collider2D otherCollider)
     {
         ShotScript shot = otherCollider.gameObject.GetComponent<ShotScript>();
         if (shot != null)
         {
             if (shot.isEnemyShot != isEnemy)
             {
                 Damage(shot.damage);
                 Destroy(shot.gameObject); // Remember to always target the game object, otherwise you will just remove the script
             }
         }
     }
 }