ui Text not responding to collider

Please help I’ve spent an entire day trying to figure this out and nothing seems to work. I am very new to Unity.

I would like for a text to pop up when I go over a certain area which is marked by a box collider on my terrain and then dissapear after 5 seconds. Everything seems to be working fine in the script as the text is not visible when I begin the game however it is never activated by the box collider. There are no error messages displayed either. I was following this tutorial: (Unity 5 - Showing Text on Trigger - YouTube)

Here is my script:

public GameObject uiObject;
void Start()
{
    uiObject.SetActive(false);
}
//Update is called once per frame
void OnTriggerEnter(Collider player)
{
    if (player.gameObject.tag == "Player")
    {
        uiObject.SetActive(true);
        StartCoroutine("WaitForSec");
    }
}

IEnumerator WaitForSec()
{
    yield return new WaitForSeconds(5);
    Destroy(uiObject);
    Destroy(gameObject);
 }

}

Use System.Collections;
In order for Coroutines to work.