For loops / lists / instantiating not working! D:

I've been having trouble with instantiating and for loops.

I have been working on a game where the player puts in coordinates for a grid and game objects are instantiated around the lengths of the grid. I have a piece of code which is NOT working and I've been stuck on it for about a week now, around a for loop based on the count of a list. I'll show the code and arguments of it down below:

( The problem is with PlaceWall() and PlaceFloor() )

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class FloorGenerator : MonoBehaviour {
 
     public GameObject floor;
     public GameObject wall;
     public GameObject landParent;
 
     List<Vector2> possibleFloorAreas = new List<Vector2>();
     public List<Vector2> possibleWallAreas = new List<Vector2>();
     List<GameObject> tileSets = new List<GameObject>();
 
     public void Start()
     {
         DiscoverAreas();
     }
 
     public void DiscoverAreas()
     {
         possibleFloorAreas.Clear();
 
         for (int r = 0; r <= CoinGenerator.instance.rows; r++)
         {
             for (int c = 0; c <= CoinGenerator.instance.collumns; c++)
             {
                 possibleFloorAreas.Add(new Vector2(c, r));
             }
         }
 
         possibleWallAreas.Clear();
 
         for (int u = -1; u <= CoinGenerator.instance.collumns + 1; u++)
         {
             possibleWallAreas.Add(new Vector2(u, -1));
             possibleWallAreas.Add(new Vector2(u, CoinGenerator.instance.rows + 1));
         }
 
         for(int o = 0; o <= CoinGenerator.instance.rows; o++)
         {
             possibleWallAreas.Add(new Vector2(-1, o));
             possibleWallAreas.Add(new Vector2(CoinGenerator.instance.collumns + 1, o));
         }
 
         PlaceFloor();
         PlaceWall();
     }
 
     public void PlaceFloor()
     {
         for(int h = 0; h <= possibleFloorAreas.Count; h++)
         {
                 GameObject theFloor = Instantiate(floor, possibleFloorAreas[h], Quaternion.identity);
                 tileSets.Add(theFloor);
                 theFloor.transform.SetParent(landParent.transform);
         }
     }
 
     public void PlaceWall()
     {
         for (int d = 0; d <= possibleWallAreas.Count; d++)
         {
             GameObject theWall = Instantiate(wall, possibleWallAreas[d], Quaternion.identity);
             tileSets.Add(theWall);
             theWall.transform.SetParent(landParent.transform);
         }
     }
     void DestroyLand()
     {
         foreach (GameObject tile in tileSets)
         {
             Destroy(tile);
         }
     }
 }

ArgumentOutOfRangeException: Argument is out of range. Parameter name: index System.Collections.Generic.List`1[UnityEngine.Vector2].get_Item (Int32 index) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/List.cs:633) FloorGenerator.PlaceFloor () (at Assets/Scripts/FloorGenerator.cs:53) FloorGenerator.DiscoverAreas () (at Assets/Scripts/FloorGenerator.cs:45) FloorGenerator.Start () (at Assets/Scripts/FloorGenerator.cs:17)

-Problem- The problem is, only the floor of the land is instantiated, the walls aren't, but the argument takes me to a part (line 53) which is the part where the floor is instantiated. The floor instantiating part is working, the wall part isn't, so I have no clue why it's taking me to the process of where the floor instantiates.

I've made the Vector 2 wall areas public in the unity editor, and when I start the game all of the vector 2 areas are found; just not used to instantiate. The wall instantiation for loop is exactly the same as the floor for loop, so I'm not sure what the problem is.

(CoinGenerator.instance.collumns/rows are just integers from another script that I'm using. They're not the problem, the problem is from instantiating with the list, not finding Vector 2's for the list)