Unity UI issues

Before anything else, I tried posting this in the correct category on the forums, but for whatever reason theres no option to post a new thread even tho I have done so before??

Anyways.

So I'm creating a simple "menu" to buy and sell things. I have started with the complete basics, and just started off by making a very very simple interface. It shows you how much money you currently have, and the option to "add 5"

I can get it to where it will show my current amount, but I keep getting this error:

 NullReferenceException: Object reference not set to an instance of an object
 GM.Start () (at Assets/Scripts/GM.cs:12)

Heres a picture of my setup + the C# code I'm working on

Can someone please help me out? I've been stuck on this a lot longer than I've wanted to be...

CODE: using UnityEngine; using UnityEngine.UI; using System.Collections;

 public class GM : MonoBehaviour 
 {
     public int startMoney = 100;
     public int addAmount = 5;
     public Text currentMoney;
 
     void Start () 
     {
         currentMoney.text = startMoney.ToString ();
     }
     
 
     void Update () 
     {
     
     }
 
     void OnBuy ()
     {
         currentMoney.text = startMoney + addAmount.ToString ();    
     }
 
 }