Instantiated clones of enemy prefab cannot be attacked?

I've set up an enemy manager to spawn clones of my enemy prefab but the spawned clones can't seem to be attacked. Here's the enemy spawn script:

 public class EnemyManager : MonoBehaviour
 {
     public PlayerHealth playerHealth;       // Reference to the player's heatlh.
     public GameObject enemy;                // The enemy prefab to be spawned.
     public float spawnTime = 3f;            // How long between each spawn.
     public Transform[] spawnPoints;         // An array of the spawn points this enemy can spawn from.
 
     void Start ()
     {
         InvokeRepeating ("Spawn", spawnTime, spawnTime);
     }
     
     
     void Spawn ()
     {
         if(playerHealth.currentHealth <= 0f)
         {
             return;
         }
         
         int spawnPointIndex = Random.Range (0, spawnPoints.Length);
         
         Instantiate (enemy, spawnPoints[spawnPointIndex].position, spawnPoints[spawnPointIndex].rotation);
     }
 }

and here's the player attack script:

 public class PlayerHit : MonoBehaviour {
     public int damagePerHit = 20;                  
     private float timeBetweenPunches = 0.15f;        
 
     float timer;                                    
     GameObject enemy;                          
     EnemyHealth enemyHealth;                    
     bool enemyInRange;
     Animator anim;
 
     void Awake () {
         enemy = GameObject.FindGameObjectWithTag ("Enemy");
         enemyHealth = enemy.GetComponent <EnemyHealth> ();
         anim = GetComponent <Animator> ();
     }
 
     void Update() {
         timer += Time.deltaTime;
         if (Input.GetKeyDown (KeyCode.F) && timer >= timeBetweenPunches) {
                         anim.Play ("punch");
                         Hit ();
                 }
         if (Input.GetKeyDown (KeyCode.G) && timer >= timeBetweenPunches) {
                         anim.Play ("hpunch");
                         Hit2 ();
                 }
         }
 
     void OnTriggerEnter (Collider other)
     {
         if (other.gameObject == enemy) {
                 enemyInRange = true;
             }
         }
 
     void OnTriggerExit (Collider other)
     {
     if (other.gameObject == enemy) {
                 enemyInRange = false;
             }
         }
 
     void Hit ()
     {
         timer = 0f;
             
             // If the EnemyHealth component exist...
         if(enemyHealth.currentHealth > 0 && enemyInRange)
         {
             // ... the enemy should take damage.
             enemyHealth.TakeDamage (damagePerHit);
     }
     }
         void Hit2 ()
         {
         timer = 0f;
             
         // If the EnemyHealth component exist...
         if (enemyHealth.currentHealth > 0 && enemyInRange) {
             // ... the enemy should take damage.
             enemyHealth.TakeDamage (30);
         }
     }
 }