Instantiate players in Photon. Error: Index was outside the bounds of the array.

I have a problem at the moment to instantiate the players in scene. I’m trying to get two players in different positions when loading the scene. But I get this error: IndexOutOfRangeException: Index was outside the bounds of the array.

What can be the problem? I understand the error which can come from the time of calling the array, but I´m a new user in unity. I hope you can help me

Thanks
This is the code

public class Septup : MonoBehaviour
{
   
    public static Septup SP;
  
    public Transform[] posiciones;

    public void OnEnable()
    {
        if (Septup.SP == null)
        {

            Septup.SP = this;


        }
    }

}

public class PlayerM : MonoBehaviour
{

    public PhotonView PL;
 
    public int aparecer;
   
    void Start()
    {
         aparecer = Septup.SP.posiciones.Length;
        PL = GetComponent<PhotonView>();
             
        if (PL.IsMine)
        {
           
            jugador = PhotonNetwork.Instantiate("P1", Septup.SP.posiciones[aparecer].position, Septup.SP.posiciones[aparecer].rotation, 0);

        }
    }

}

when you have an issue with an error always add the line the error occures in.
Other than that your problem is that you have an array and you try to call The index of Length.
If you have an array with 2 elements the Length is 2 but the last element has the index 1.
You simply have to subtract 1.