RigidbodyFirstPersonController and external forces...

Hi, I'm using the RigidbodyFirstPersonController prefab in a shooting game.

I have some zombies with NavMeshAgents attacking the player. In the zombie script I have this method:

 public void PlayerSpotted(Collider player)
     {
         Vector3 playerPos = player.transform.position;
         state = State.FOLLOWING;
         agent.SetDestination(playerPos);
 
         if (CanAttack && Vector3.Distance(playerPos, transform.position) <= AttackRange)
         {
             animator.SetTrigger("attack");
             player.attachedRigidbody.AddExplosionForce(100, transform.position, 10, transform.position.y, ForceMode.Impulse);
         }
     }

but the player doesn't move at all.

I tried changing the intensity of the force, but nothing happens. I guess the problem is with the RigidbodyFPS component but I can't help with it. Any clue?