Button OnClick not displaying in inspector

When I assign the OnClick from Start(), OnEnable() or Reset(). it does not show in the inspector. The event fires just fine but is not showing in inspector. The OnClick for the button still says emtpy after starting the game. In the code below the OKButton is assigned from another script. Its definitely not coming back null.

 public Button OKButton;
 
     // Use this for initialization
     void Start()
     {
         if (OKButton != null)
         {
             OKButton.onClick.AddListener(delegate { OKButton_OnClick(); });
         }
     }
     void OKButton_OnClick()
     {
         Debug.Log("Test");
     }