input issues

I'am new to coding, and i'm having issues with a script i'm working with. The script is a detection script that lets me open doors and close them within my current project. The issue i'm having is that I need to use a GUI button for the door to open but the script is designed to work with a keyboard input. I've tried using Input.GetButtonDown and it doesn't seem to work. Here's the script for example

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 public class Detection : MonoBehaviour
 {
     // INSPECTOR SETTINGS
     [Header("Detection Settings")]
     [Tooltip("Within this radius the player is able to open/close the door")]
     public float Reach = 4F;
     [Tooltip("The tag that triggers the object to be openable")]
     public string TriggerTag = "Door";
 
     // PRIVATE SETTINGS
     [HideInInspector] public bool InReach;
 
     //DEBUGGING (DEBUG PANEL)
     [Header("Debug Settings")]
     public Color DebugRayColor = Color.green;
     public bool InGameDebugger = false;
 
     string CategoryDetection = "Detection";
     string TitleReach = "Reach";
     string TitleInReach = "InReach";
 
     string CategoryDoor = "Door";
     string TitleHitTag = "HitTag";
     string TitleHingeSide = "HingeSide";
     string TitleCurrentAngle = "CurrentAngle";
     string TitleSpeed = "Speed";
     string TitleTimesMoveable = "TimesMoveable";
     string TitleRunning = "Running";
 
     //START FUNCTION
     void Start()
     {
 
     }
 
     //UPDATE FUNCTION
     void Update()
     {
         // Set origin of ray to 'center of screen' and direction of ray to 'cameraview'.
         Ray ray = Camera.main.ViewportPointToRay (new Vector3 (0.5F, 0.5F, 0F));
 
         RaycastHit hit; // Variable reading information about the collider hit.
 
         // Cast a ray from the center of screen towards where the player is looking.
         if (Physics.Raycast (ray, out hit, Reach))
         {
             //DEBUGGING (DEBUG PANEL)
             DebugPanel.Log(TitleHitTag, CategoryDoor, hit.collider.tag);
 
             if(hit.collider.tag == TriggerTag)
             {
                 InReach = true;
 
                 if (Input.GetButtonDown("Open/Close"))
                     
                 {
                     // Give the object that was hit the name 'Door'.
                     GameObject Door = hit.transform.gameObject;
 
                     // Get access to the 'DoorOpening' script attached to the door that was hit.
                     Door dooropening = Door.GetComponent<Door>();
 
                     // Check whether the door is opening/closing or not.
                     if (dooropening.Running == false)
                     {
                         // Open/close the door by running the 'Open' function in the 'DoorOpening' script.
                         StartCoroutine (hit.collider.GetComponent<Door>().Open());
                     }
                 }
             }
 
             else InReach = false;
 
         }
 
         else
         {
             InReach = false;
 
             //DEBUGGING (DEBUG PANEL)
             DebugPanel.Break(TitleHitTag);
         }
 
         //DEBUGGING (DEBUG PANEL)
         DebugPanel.Log(TitleInReach, CategoryDetection, InReach);
         DebugPanel.Log(TitleReach, CategoryDetection, Reach);
 
         if (InReach == true)
         {
             DebugPanel.Log (TitleHingeSide, CategoryDoor, hit.collider.GetComponent<Door>().HingeSide);
             DebugPanel.Log (TitleSpeed, CategoryDoor, hit.collider.GetComponent<Door> ().Speed);
             DebugPanel.Log (TitleTimesMoveable, CategoryDoor, hit.collider.GetComponent<Door> ().TimesMoveable);
             DebugPanel.Log (TitleCurrentAngle, CategoryDoor, Mathf.Round(hit.transform.eulerAngles.y) + "°");
             DebugPanel.Log (TitleRunning, CategoryDoor, hit.collider.GetComponent<Door> ().Running);
         }
 
         else
         {
             DebugPanel.Break (TitleHingeSide);
             DebugPanel.Break (TitleSpeed);
             DebugPanel.Break (TitleTimesMoveable);
             DebugPanel.Break (TitleCurrentAngle);
             DebugPanel.Break (TitleRunning);
         }
 
         // Draw the ray as a colored line for debugging purposes.
         Debug.DrawRay (ray.origin, ray.direction*Reach, DebugRayColor);
     }
 }